dt-bindings: video: Add documentation for rockchip vop

This adds binding documentation for Rockchip SoC VOP driver.
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>

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

+device-tree bindings for rockchip soc display controller (vop)
+
+VOP (Visual Output Processor) is the Display Controller for the Rockchip
+series of SoCs which transfers the image data from a video memory
+buffer to an external LCD interface.
+
+Required properties:
+- compatible: value should be one of the following
+		"rockchip,rk3288-vop";
+
+- interrupts: should contain a list of all VOP IP block interrupts in the
+		 order: VSYNC, LCD_SYSTEM. The interrupt specifier
+		 format depends on the interrupt controller used.
+
+- clocks: must include clock specifiers corresponding to entries in the
+		clock-names property.
+
+- clock-names: Must contain
+		aclk_vop: for ddr buffer transfer.
+		hclk_vop: for ahb bus to R/W the phy regs.
+		dclk_vop: pixel clock.
+
+- resets: Must contain an entry for each entry in reset-names.
+  See ../reset/reset.txt for details.
+- reset-names: Must include the following entries:
+  - axi
+  - ahb
+  - dclk
+
+- iommus: required a iommu node
+
+- port: A port node with endpoint definitions as defined in
+  Documentation/devicetree/bindings/media/video-interfaces.txt.
+
+Example:
+SoC specific DT entry:
+	vopb: vopb@ff930000 {
+		compatible = "rockchip,rk3288-vop";
+		reg = <0xff930000 0x19c>;
+		interrupts = <GIC_SPI 15 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cru ACLK_VOP0>, <&cru DCLK_VOP0>, <&cru HCLK_VOP0>;
+		clock-names = "aclk_vop", "dclk_vop", "hclk_vop";
+		resets = <&cru SRST_LCDC1_AXI>, <&cru SRST_LCDC1_AHB>, <&cru SRST_LCDC1_DCLK>;
+		reset-names = "axi", "ahb", "dclk";
+		iommus = <&vopb_mmu>;
+		vopb_out: port {
+			#address-cells = <1>;
+			#size-cells = <0>;
+			vopb_out_edp: endpoint@0 {
+				reg = <0>;
+				remote-endpoint=<&edp_in_vopb>;
+			};
+			vopb_out_hdmi: endpoint@1 {
+				reg = <1>;
+				remote-endpoint=<&hdmi_in_vopb>;
+			};
+		};
+	};