dt-bindings: Add documentation for rockchip dw hdmi

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Documentation/devicetree/bindings/video/dw_hdmi-rockchip.txt

+Rockchip specific extensions to the Synopsys Designware HDMI
+================================
+
+Required properties:
+- compatible: "rockchip,rk3288-dw-hdmi";
+- reg: Physical base address and length of the controller's registers.
+- clocks: phandle to hdmi iahb and isfr clocks.
+- clock-names: should be "iahb" "isfr"
+- rockchip,grf: this soc should set GRF regs to mux vopl/vopb.
+- interrupts: HDMI interrupt number
+- ports: contain a port node with endpoint definitions as defined in
+  Documentation/devicetree/bindings/media/video-interfaces.txt. For
+  vopb,set the reg = <0> and set the reg = <1> for vopl.
+- reg-io-width: the width of the reg:1,4, the value should be 4 on
+  rk3288 platform
+
+Optional properties
+- ddc-i2c-bus: phandle of an I2C controller used for DDC EDID probing
+- clocks, clock-names: phandle to the HDMI CEC clock, name should be "cec"
+
+Example:
+hdmi: hdmi@ff980000 {
+	compatible = "rockchip,rk3288-dw-hdmi";
+	reg = <0xff980000 0x20000>;
+	reg-io-width = <4>;
+	ddc-i2c-bus = <&i2c5>;
+	rockchip,grf = <&grf>;
+	interrupts = <GIC_SPI 103 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&cru  PCLK_HDMI_CTRL>, <&cru SCLK_HDMI_HDCP>;
+	clock-names = "iahb", "isfr";
+	status = "disabled";
+	ports {
+		hdmi_in: port {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			hdmi_in_vopb: endpoint@0 {
+				reg = <0>;
+				remote-endpoint = <&vopb_out_hdmi>;
+			};
+			hdmi_in_vopl: endpoint@1 {
+				reg = <1>;
+				remote-endpoint = <&vopl_out_hdmi>;
+			};
+		};
+	};
+};