gpio-backlight bindings

Required properties:
  - compatible: "gpio-backlight"
  - gpios: describes the gpio that is used for enabling/disabling the backlight.
    refer to bindings/gpio/gpio.txt for more details.

Optional properties:
  - default-on: enable the backlight at boot.

Example:
	backlight {
		compatible = "gpio-backlight";
		gpios = <&gpio3 4 GPIO_ACTIVE_HIGH>;
		default-on;
	};