Doc/DT: Add DT binding documentation for TFP410 encoder

TFP410 DPI to DVI encoder

=========================

Required properties:

- compatible: "ti,tfp410"

Optional properties:

- powerdown-gpios: power-down gpio

Required nodes:

- Video port 0 for DPI input

- Video port 1 for DVI output

Example

-------

tfp410: encoder@0 {

	compatible = "ti,tfp410";

	powerdown-gpios = <&twl_gpio 2 GPIO_ACTIVE_LOW>;

	ports {

		#address-cells = <1>;

		#size-cells = <0>;

		port@0 {

			reg = <0>;

			tfp410_in: endpoint@0 {

				remote-endpoint = <&dpi_out>;

			};

		};

		port@1 {

			reg = <1>;

			tfp410_out: endpoint@0 {

				remote-endpoint = <&dvi_connector_in>;

			};

		};

	};

};