ps8640-bridge bindings

Required properties:
	- compatible: "parade,ps8640"
	- reg: first page address of the bridge.
	- sleep-gpios: OF device-tree gpio specification for PD pin.
	- reset-gpios: OF device-tree gpio specification for reset pin.
	- vdd12-supply: OF device-tree regulator specification for 1.2V power.
	- vdd33-supply: OF device-tree regulator specification for 3.3V power.
	- ports: The device node can contain video interface port nodes per
		 the video-interfaces bind[1]. For port@0,set the reg = <0> as
		 ps8640 dsi in and port@1,set the reg = <1> as ps8640 eDP out.

Optional properties:
	- mode-sel-gpios: OF device-tree gpio specification for mode-sel pin.
[1]: Documentation/devicetree/bindings/media/video-interfaces.txt

Example:
	edp-bridge@18 {
		compatible = "parade,ps8640";
		reg = <0x18>;
		sleep-gpios = <&pio 116 GPIO_ACTIVE_LOW>;
		reset-gpios = <&pio 115 GPIO_ACTIVE_LOW>;
		mode-sel-gpios = <&pio 92 GPIO_ACTIVE_HIGH>;
		vdd12-supply = <&ps8640_fixed_1v2>;
		vdd33-supply = <&mt6397_vgp2_reg>;

		ports {
			#address-cells = <1>;
			#size-cells = <0>;
			port@0 {
				reg = <0>;
				ps8640_in: endpoint {
					remote-endpoint = <&dsi0_out>;
				};
			};
			port@1 {
				reg = <1>;
				ps8640_out: endpoint {
					remote-endpoint = <&panel_in>;
				};
			};
		};
	};