pwm-backlight bindings

Required properties:
  - compatible: "pwm-backlight"
  - pwms: OF device-tree PWM specification (see PWM binding[0])
  - brightness-levels: Array of distinct brightness levels. Typically these
      are in the range from 0 to 255, but any range starting at 0 will do.
      The actual brightness level (PWM duty cycle) will be interpolated
      from these values. 0 means a 0% duty cycle (darkest/off), while the
      last value in the array represents a 100% duty cycle (brightest).
  - default-brightness-level: the default brightness level (index into the
      array defined by the "brightness-levels" property)

Optional properties:
  - pwm-names: a list of names for the PWM devices specified in the
               "pwms" property (see PWM binding[0])

[0]: Documentation/devicetree/bindings/pwm/pwm.txt

Example:

	backlight {
		compatible = "pwm-backlight";
		pwms = <&pwm 0 5000000>;

		brightness-levels = <0 4 8 16 32 64 128 255>;
		default-brightness-level = <6>;
	};