devicetree: Add new SKY81452 backlight binding

Signed-off-by: Gyungoh Yoo <jack.yoo@skyworksinc.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/video/backlight/sky81452-backlight.txt

+SKY81452-backlight bindings
+
+Required properties:
+- compatible		: Must be "skyworks,sky81452-backlight"
+
+Optional properties:
+- name			: Name of backlight device. Default is 'lcd-backlight'.
+- gpios			: GPIO to use to EN pin.
+			See Documentation/devicetree/bindings/gpio/gpio.txt
+- led-sources		: List of enabled channels from 0 to 5.
+			See Documentation/devicetree/bindings/leds/common.txt
+- skyworks,ignore-pwm	: Ignore both PWM input
+- skyworks,dpwm-mode	: Enable DPWM dimming mode, otherwise Analog dimming.
+- skyworks,phase-shift	: Enable phase shift mode
+- skyworks,short-detection-threshold-volt
+			: It should be one of 4, 5, 6 and 7V.
+- skyworks,current-limit-mA
+			: It should be 2300mA or 2750mA.
+
+Example:
+
+	backlight {
+		compatible = "skyworks,sky81452-backlight";
+		name = "pwm-backlight";
+		led-sources = <0 1 2 5>;
+		skyworks,ignore-pwm;
+		skyworks,phase-shift;
+		skyworks,current-limit-mA = <2300>;
+	};