dt-bindings: msm: Add document for fan driver on RB5

Qualcomm Technologies, Inc. QRB5165 Fan Controller Driver

This binding describes the QRB5165 Fan Controller Driver, it controls

fan with pm8150l gpio 10.

- compatible:

	Usage: required

	Value type: <stringlist>

	Definition: must be "qcom,rb5_fan_controller"

- qcom,pwr-enable-gpio:

	Usage: required

	Value type: <prop-encoded-array>

	Definition: the gpio to enable fan pwr

Example:

	rb5_fan_controller {

		compatible = "qcom,rb5_fan_controller";

		qcom,pwr-enable-gpio = <&pm8150l_gpios 10 0x0>;

		pinctrl-name = "default";

		pinctrl-0 = <&rb5_fan_controller_pin_init>;

		status = "ok";

	};