88pm860x-backlight bindings

Optional properties:
  - marvell,88pm860x-iset: Current supplies on backlight device.
  - marvell,88pm860x-pwm: PWM frequency on backlight device.

Example:

	backlights {
		backlight-0 {
			marvell,88pm860x-iset = <4>;
			marvell,88pm860x-pwm = <3>;
		};
		backlight-2 {
		};