Thermal estimator driver.

Properties :
 - compatible : Should contain "nvidia,therm-est".
 - polling-period : Polling wait times for thermal estimation, in milliseconds.
 - tc1 : Coefficient 1 for thermal trend calculation.
 - tc2 : Coefficient 2 for thermal trend calculation.
 - node for subdev : Node for subdevice information. Required.
 - use_tmargin : if tmargin algorithm should be used for calculating the
   effective temp. Refer Tmargin section for more info.

Properties in subdev node : Required.
 - subdev_names : list of strings. It contains list of the name of the therm
		zones used for estimation.
 - node for coeff_set : contains a set of zone specific coefficients+offset.
			This node can be numerous.

Properties in coeff_set : Required. Can be numerous.
 - toffset : Temperature offset for thermal estimation, in milli-celsius.
 - coeffs : An array of coefficients, the number of entries should be twenty
	per sub device.

Example:

	therm_est_sensor {
		device_type = "therm-est-subdev";
		polling-period = <1100>;
		tc1 = <10>;
		tc2 = <1>;
		subdev {
			subdev_names = "Tdiode_tegra", "Tboard_tegra";

			coeff_set@0 {
				toffset = <9793>;
				coeffs = <
					2 1 1 1 1 1 1 1 1 1 1 0 1 1 0 0 0 0 (-1) (-7)
					(-11) (-7) (-5) (-3) (-3) (-2) (-1) 0 0 0 1 1 1 2 2 3 4 6 11 18
				>;
			};

			coeff_set@1 {
				toffset = <708>;
				coeffs = <
					-1 -1 1 1 1 1 1 1 1 1 1 0 1 1 0 0 0 (-1) (-3) (-9)
					(-6) (-4) (-1) 0 0 0 0 0 0 0 1 1 1 2 2 5 7 10 17 20
				>;
			};
		};
	};

Tmargin Algorithm:
The native max temp algorithm lacks support for accomodating multiple thermal
fan curves. Tmargin algorithm solves this by calculating the effective
temperature as a difference from critical temperature of the therm fan est
group. This allows us to take a union of two fan curves and satisfy the needs
of both the therm-fan-est groups.
The algorithm use the effective temperature(crit_temp - sensor_reading) to
drive the cooling device.

Properties rules for therm-fan-est dt entry:
 - use_tmargin : To use the tmargin feature.
 - profiles : New profile tmargin should be defined and chosen as default.
	* The trip temperatures need to be given only in ascending order for the
	  thermal framework to register therm-fan-est zone. Hence, the dt values
	  for active trip temps should be given in ascending values of tmargin
	  values.
	* Hysterysis is used only in cooling scenario. Since tmargin is
	  considered as a diff wrt crit_Temp, hysterysis values should be taken
	  as -ve values.

Properties rules for fan dt entry:
 - profiles : New profile for tmargin should be defined and chosen as default.
	* The trip temps are considered in a ascending order of tmargin temps.
	  Hence, the pwm values should be considered in a descending order of
	  pwms.
	* active_steps - The tmargin trip values are considered in the ascending
	  order(hence actual trip temps will be in descending order), so the
	  pwm mapping should be in the reverse order starting from 255 for
	  index 0.

Example :

        thermal-fan-est {
                compatible = "thermal-fan-est";
                name = "thermal-fan-est";
                status = "okay";
                num_resources = <0>;
                shared_data = <&thermal_fan_est_shared_data>;
                trip_length = <10>;
                use_tmargin;

                profiles {
                        default = "tmargin";
                        quiet {
                                active_trip_temps = <0 50000 63000 72000 81000
                                                140000 150000 160000 170000 180000>;
                                active_hysteresis = <0 18000 8000 8000 8000
                                                0 0 0 0 0>;
                        };
                        cool {
                                active_trip_temps = <0 35000 53000 62000 73000
                                                140000 150000 160000 170000 180000>;
                                active_hysteresis = <0 9000 8000 8000 9000
                                                0 0 0 0 0>;
                        };
                        tmargin {
                                active_trip_temps = <0 10000 15000 25000 35000
                                                45000 55000 65000 75000 105000>;
                                active_hysteresis = <0 0 0 0 (-3000)
                                                (-4000) (-4000) 0 0 0>;
                        };
                };
        };

        pwm-fan {
                compatible = "pwm-fan";
                status = "okay";
                #pwm-cells = <1>;
                pwms = <&tegra_pwm4 0 45334>;
                shared_data = <&pwm_fan_shared_data>;
                profiles {
                        default = "tmargin";
                        quiet {
                                state_cap = <8>;
                                active_pwm = <0 60 90 120 150 180 210 240 255 255>;
                        };
                        cool {
                                state_cap = <4>;
                                active_pwm = <0 77 120 160 255 255 255 255 255 255>;
                        };
                        tmargin {
                                state_cap = <0>;
                                active_pwm = <255 255 240 210 180 150 120 90 60 0>;
                        };
                };
        };