Device-Tree bindings for Xilinx ZynqMP DisplayPort Audio Card

The card driver integrates codec and pcm components and represents as a single
audio device.

Required properties:
 - compatible: Should be "xlnx,dp-snd-card".
 - xlnx,dp-snd-pcm: phandle(s) to the ZynqMP DP PCM node.
 - xlnx,dp-snd-codec: phandle to the ZynqMP DP card node.

Example:

	xlnx_dp_snd_card: dp_snd_card {
		compatible = "xlnx,dp-snd-card";
		xlnx,dp-snd-pcm = <&xlnx_dp_snd_pcm0>, <&xlnx_dp_snd_pcm1>;
		xlnx,dp-snd-codec = <&xlnx_dp_snd_codec0>;
	};
