drm/tve200: Add DT bindings

This adds device tree bindings for the Faraday TVE200 IP block.
This IP block is present in the Gemini ARM SoC and also in some
Grain Media GMxxxx SoCs.

Cc: [e-mail]
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/devicetree/bindings/display/faraday,tve200.txt

···
+* Faraday TV Encoder TVE200
+
+Required properties:
+
+- compatible: must be one of:
+	"faraday,tve200"
+	"cortina,gemini-tvc", "faraday,tve200"
+
+- reg: base address and size of the control registers block
+
+- interrupts: contains an interrupt specifier for the interrupt
+	line from the TVE200
+
+- clock-names: should contain "PCLK" for the clock line clocking the
+	silicon and "TVE" for the 27MHz clock to the video driver
+
+- clocks: contains phandle and clock specifier pairs for the entries
+	in the clock-names property. See
+	Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+Optional properties:
+
+- resets: contains the reset line phandle for the block
+
+Required sub-nodes:
+
+- port: describes LCD panel signals, following the common binding
+	for video transmitter interfaces; see
+	Documentation/devicetree/bindings/media/video-interfaces.txt
+	This port should have the properties:
+	reg = <0>;
+	It should have one endpoint connected to a remote endpoint where
+	the display is connected.
+
+Example:
+
+display-controller@6a000000 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+	compatible = "faraday,tve200";
+	reg = <0x6a000000 0x1000>;
+	interrupts = <13 IRQ_TYPE_EDGE_RISING>;
+	resets = <&syscon GEMINI_RESET_TVC>;
+	clocks = <&syscon GEMINI_CLK_GATE_TVC>,
+		 <&syscon GEMINI_CLK_TVC>;
+	clock-names = "PCLK", "TVE";
+
+	port@0 {
+		reg = <0>;
+		display_out: endpoint {
+			remote-endpoint = <&panel_in>;
+		};
+	};
+};