dt-bindings: add documentation for max31760 fancontroller

Bindings for the Maxim MAX31760 Intelligent Fan Controller

==========================================================

The Maxim MAX31760 is a i2c device providing closed-loop, multi-channel fan

management with temperature. Various fan control features are provided,

including PWM frequency control, temperature hysteresis, dual tachometer

measurements, and fan health monitoring.

Required properties:

- compatible         : should be "maxim,max31760".

- reg                : I2C address, 0x50.

Optional properties:

- maxim,vdd-supply   : regulator supplying the vdd pin

- maxim,vdd-max-uv   : regulator max voltage

- maxim,vdd-min-uv   : regulator min voltage

- maxim,vdd-load-ua  : regulator load current output

- maxim,vcca-supply  : regulator supplying the vcca pin

- maxim,vcca-max-uv  : regulator max voltage

- maxim,vcca-min-uv  : regulator min voltage

- maxim,vcca-load-ua : regulator load current output

- maxim,fan_en_gpio  : fan enable gpio

Example:

	max31760@50 {

		compatible = "maxim,max31760";

		reg = <0x50>;

		maxim,vdd-supply = <&some_reg>;

		regulator-names = "maxim,vdd";

		maxim,vdd-max-uv = <3400000>;

		maxim,vdd-min-uv = <3300000>;

		maxim,vdd-load-ua = <300000>;

		maxim,vcca-supply = <&some_reg>;

		maxim,vcca-max-uv = <1800000>;

		maxim,vcca-min-uv = <1800000>;

		maxim,vcca-load-ua = <600000>;

		maxim,fan_en_gpio = <&tlmm 10 0x00>;

	};