[media] dt-bindings: Document the Rockchip RGA bindings

Add DT bindings documentation for Rockchip RGA

Signed-off-by: Jacob Chen <[e-mail]>
Signed-off-by: Yakir Yang <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/devicetree/bindings/media/rockchip-rga.txt

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+device-tree bindings for rockchip 2D raster graphic acceleration controller (RGA)
+
+RGA is a standalone 2D raster graphic acceleration unit. It accelerates 2D
+graphics operations, such as point/line drawing, image scaling, rotation,
+BitBLT, alpha blending and image blur/sharpness.
+
+Required properties:
+- compatible: value should be one of the following
+		"rockchip,rk3288-rga";
+		"rockchip,rk3399-rga";
+
+- interrupts: RGA interrupt specifier.
+
+- clocks: phandle to RGA sclk/hclk/aclk clocks
+
+- clock-names: should be "aclk", "hclk" and "sclk"
+
+- resets: Must contain an entry for each entry in reset-names.
+  See ../reset/reset.txt for details.
+- reset-names: should be "core", "axi" and "ahb"
+
+Example:
+SoC-specific DT entry:
+	rga: rga@ff680000 {
+		compatible = "rockchip,rk3399-rga";
+		reg = <0xff680000 0x10000>;
+		interrupts = <GIC_SPI 55 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cru ACLK_RGA>, <&cru HCLK_RGA>, <&cru SCLK_RGA_CORE>;
+		clock-names = "aclk", "hclk", "sclk";
+
+		resets = <&cru SRST_RGA_CORE>, <&cru SRST_A_RGA>, <&cru SRST_H_RGA>;
+		reset-names = "core, "axi", "ahb";
+	};