video: Add ADV7123 DT bindings documentation

Analog Device ADV7123 Video DAC

-------------------------------

The ADV7123 is a digital-to-analog converter that outputs VGA signals from a

parallel video input.

Required properties:

- compatible: Should be "adi,adv7123"

Optional properties:

- psave-gpios: Power save control GPIO

Required nodes:

The ADV7123 has two video ports. Their connections are modeled using the OF

graph bindings specified in Documentation/devicetree/bindings/graph.txt.

- Video port 0 for DPI input

- Video port 1 for VGA output

Example

-------

	adv7123: encoder@0 {

		compatible = "adi,adv7123";

		ports {

			#address-cells = <1>;

			#size-cells = <0>;

			port@0 {

				reg = <0>;

				adv7123_in: endpoint@0 {

					remote-endpoint = <&dpi_out>;

				};

			};

			port@1 {

				reg = <1>;

				adv7123_out: endpoint@0 {

					remote-endpoint = <&vga_connector_in>;

				};

			};

		};

	};