Device-Tree bindings for Phytium simple encoder

Simple encoder driver only has basic functionality

Required properties:
- compatible: should be one of the following:
		"phytium,hdmi-encoder"
		"phytium,dp-encoder"
		"phytium,dsi-encoder"

- ports: contain a port nodes with endpoint definitions as defined in
	 Documentation/devicetree/bindings/media/video-interfaces.txt.

Optional properties:
- phytium,dss-syscon: contains a phandle to a syscon device. When this
	one is used, the options below is mandatory.
	Reference to Documentation/devicetree/bindings/mfd/syscon.txt.

- phytium,mux-mask: mask array to access register, the index id should be
	corresponded to active crtc as defined in port@0.
- phytium,mux-val: val array to write to register, the index id should be
	corresponded to active crtc as defined in port@0.

Example1:

dssctrl: dssctrl@9000000 {
	compatible = "phytium,dss-ctrl", "syscon";
	reg = <0 0x9000000 0 0x90>;
};

hdmi_output: hdmi-output {
	compatible = "phytium,hdmi-encoder";
	phytium,dss-syscon = <&dssctrl>;
	phytium,mux-mask = <0x70 0x380>;
	phytium,mux-val = <0x40 0x280>;
	ports {
		#address-cells = <1>;
		#size-cells = <0>;
		/* input */
		port@0 {
			#address-cells = <1>;
			#size-cells = <0>;
			reg = <0>;
			hdmi_input0:endpoint@0 {
				reg = <0>;
				remote-endpoint = <&dc0_out_dpi0>;
			};
			hdmi_input1:endpoint@1 {
				reg = <1>;
				remote-endpoint = <&dc1_out_dpi0>;
			};
		};
		/* output */
		port@1 {
			reg = <1>;
			hdmi_out:endpoint {
				remote-endpoint = <&adv7511_input>;
			};
		};
	};
};

Example2:

hdmi_output: hdmi-output {
	compatible = "phytium,hdmi-encoder";

	ports {
		#address-cells = <1>;
		#size-cells = <0>;
		/* input */
		port@0 {
			#address-cells = <1>;
			#size-cells = <0>;
			reg = <0>;
			hdmi_input0:endpoint@0 {
				reg = <0>;
				remote-endpoint = <&dc0_out_dpi0>;
			};
		};
		/* output */
		port@1 {
			reg = <1>;
			hdmi_out:endpoint {
				remote-endpoint = <&adv7511_input>;
			};
		};
	};
};
