Bindings for a fan connected to the PWM lines

Properties details:
- compatible		: "pwm-fan"
- pwms			: the PWM that is used to control the PWM fan

- shared_data
  - active_steps	: Entries for references in active_rpm[], active_pwm[], active_rru[], active_rrd[]
  - active_rru		: This value is kept on added to cur_pwm till it reaches at
			  next active step from the table. This is repeated until cur_pwm
			  value reaches target_pwm
  - active_rrd		: This value is kept on subtracted from cur_pwm till it reaches at
			  previous active step from the table. This is repeated until cur_pwm
			  value reaches target_pwm
  - state_cap_lookup 	: Index to refer in active_pwm[]
  - pwm_period		: To derive duty cycle
  - pwm_id		: Assigned PWM controller id to tegra fan
			  Same as mentioned id in pwms. In pwms, the id starts from 1
			  pwm_id in pfsd, the id starts from 0
  - step_time		: Time taken for each step during rru/rrd
  - state_cap		: Capping state value out of available active_steps
  - active_pwm_max	: Max pwm value (256)
  - pwm_gpio		: GPIO pin used for pwm
  - use_tach_feedback   : Enable the tachometer feedback logic. If a pwm set
			  request is raised, two worker threads are scheduled.
			  One for setting the pwm value and one for correcting
			  the pwm based on desired rpm for the pwm requested.
			  The tachometer readings are validated for 16 consecutive times
			  before the feedbacklogic bails out successfully.
			  If the rpm validation fails, the second worker thread
			  keeps updating the pwm using the rru/rrd values.
  - rpm_ramp_time_ms	: The rpm validation worker thread waits for the given
			  value(milliseconds) after scheduling the pwm  set
			  worker thread.
  - rpm_diff_tolerance  : How much rpm diff is to be tolerated by the rpm
			  validation logic.
  - rpm_valid_retry_count : In case the fan rpm is in limit, how many times
			    should the validation logic test for regression.
  - rpm_valid_retry_delay : How much delay to be used during the validation
			    retries after the rpm is brought to threshold values
  - rpm_invalid_retry_delay : In case the rpm expected and tachometer reading
			      values mismatch, how much delay should be used for
			      next validation.
  - use_tmargin		: If Tmargin algorithm is being used in therm_fan_est
    			  driver. This node needs to be enabled for the pwm fan
			  driver to work properly.
  - is_always_on	: Enable if the fan is always on.

Example:

	pwm_fan_shared_data: pfsd {
		status = "okay";
		num_resources = <0>;
		active_steps = <10>;
		active_rpm = <0 1000 2000 3000 4000 5000 6000 7000 10000 11000>;
		active_rru = <40 2 1 1 1 1 1 1 1 1>;
		active_rrd = <40 2 1 1 1 1 1 1 1 1>;
		state_cap_lookup = <2 2 2 2 3 3 3 4 4 4>;
		pwm_period = <45334>;
		pwm_id = <3>;
		step_time = <100>; /* mesecs */
		state_cap = <7>;
		active_pwm_max = <256>;
		pwm_gpio = <&tegra_aon_gpio TEGRA_AON_GPIO(V, 6) GPIO_ACTIVE_LOW>; /* TEGRA_MAIN_GPIO_PV6 */
	};
	pwm-fan {
		status = "okay";
		compatible = "pwm-fan";
		#pwm-cells = <1>;
		pwms = <&tegra_pwm4 0 45334>;
		shared_data = <&pwm_fan_shared_data>;
		active_pwm = <0 80 120 160 255 255 255 255 255 255>;
	};
};