Device-Tree bindings for Xilinx SDI Tx IP core

The IP core supports transmission of video data in SDI Tx: protocol.

Required properties:
 - compatible: Should be "xlnx,v-smpte-uhdsdi-tx-ss".
 - interrupts: Interrupt number.
 - interrupts-parent: phandle for interrupt controller.
 - reg: Base address and size of the IP core.
 - ports: Connects to the drm device node through device graph binding.
   The port should contain a 'remote-endpoint' subnode that points to the
   endpoint in the port of the drm device node. Refer to
   Documentation/devicetree/bindings/graph.txt.
 - xlnx,vtc: vtc phandle

Example:

		v_smpte_uhdsdi_tx_ss: v_smpte_uhdsdi_tx_ss@80020000 {
			compatible = "xlnx,v-smpte-uhdsdi-tx-ss";
			interrupt-parent = <&gic>;
			interrupts = <0 90 4>;
			reg = <0x0 0x80020000 0x0 0x10000>;
			xlnx,vtc = <&v_tc_0>;
			ports {
				#address-cells = <1>;
				#size-cells = <0>;
				port@0 {
					reg = <0>;
					sdi_port: endpoint {
						remote-endpoint = <&drm_port>;
					};
				};
		        };
		};
