dt-bindings: leds: Add document bindings for leds-mt6323

This patch adds documentation for devicetree bindings for LED support on
MT6323 PMIC.
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>

Documentation/devicetree/bindings/leds/leds-mt6323.txt

+Device Tree Bindings for LED support on MT6323 PMIC
+
+MT6323 LED controller is subfunction provided by MT6323 PMIC, so the LED
+controllers are defined as the subnode of the function node provided by MT6323
+PMIC controller that is being defined as one kind of Muti-Function Device (MFD)
+using shared bus called PMIC wrapper for each subfunction to access remote
+MT6323 PMIC hardware.
+
+For MT6323 MFD bindings see:
+Documentation/devicetree/bindings/mfd/mt6397.txt
+For MediaTek PMIC wrapper bindings see:
+Documentation/devicetree/bindings/soc/mediatek/pwrap.txt
+
+Required properties:
+- compatible : Must be "mediatek,mt6323-led"
+- address-cells : Must be 1
+- size-cells : Must be 0
+
+Each led is represented as a child node of the mediatek,mt6323-led that
+describes the initial behavior for each LED physically and currently only four
+LED child nodes can be supported.
+
+Required properties for the LED child node:
+- reg : LED channel number (0..3)
+
+Optional properties for the LED child node:
+- label : See Documentation/devicetree/bindings/leds/common.txt
+- linux,default-trigger : See Documentation/devicetree/bindings/leds/common.txt
+- default-state: See Documentation/devicetree/bindings/leds/common.txt
+
+Example:
+
+	mt6323: pmic {
+		compatible = "mediatek,mt6323";
+
+		...
+
+		mt6323led: leds {
+			compatible = "mediatek,mt6323-led";
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			led@0 {
+				reg = <0>;
+				label = "LED0";
+				linux,default-trigger = "timer";
+				default-state = "on";
+			};
+			led@1 {
+				reg = <1>;
+				label = "LED1";
+				default-state = "off";
+			};
+			led@2 {
+				reg = <2>;
+				label = "LED2";
+				default-state = "on";
+			};
+		};
+	};