MAX77812 voltage regulator

Required properties:
- compatible: "maxim,max77812-regulator"
- reg: I2C slave address

Regulators subnode:

MAX77812 supports four regulators, regulators should be described under
    regualtors subnode.

Optional properties:
-maxim,ramp-up-slew-rate: to configure slew rate during regulator
	 voltage ramp up time
-maxim,ramp-down-slew-rate: to configre slew rate during regulator
	 voltage ramp down time
-maxim,soft-start-slew-rate: to configure slew rate during regulator
	enable time
-maxim,shutdown-slew-rate: to configure slew rate during regulator
	disable time or shutdown time

Each regulator is defined using the standard binding for regulators.

Example:

	max77812@1b {
		compatible = "maxim,max77812-regulator";
		reg = <0x1b>;

		regulators {
			m1vout {
				regulator-name = "mvout1";
				regulator-min-microvolt = <250000>;
				regulator-max-microvolt = <1525000>;
				regulator-boot-on;
				regulator-always-on;
				regulator-init-mode = <REGULATOR_MODE_NORMAL>;
			};

			m2vout {
				regulator-name = "mvout2";
				regulator-always-on;
				regulator-boot-on;
				regulator-min-microvolt = <250000>;
				regulator-max-microvolt = <1525000>;
				regulator-init-mode = <REGULATOR_MODE_NORMAL>;
			};
		};
	};