* Spreadtrum asoc machine driver of i2s

This node models the spreadtrum ASoC machine driver

Required properties:
- compatible		: "sprd,i2s-null-codec", "sprd,vbc-r3p0-codec-sc2731",
				"sprd,vbc-r1p0v3-codec-sc2721", "sprd,vbc-r1p0v3-codec-sc2731",
				"sprd,vbc-r2p0-codec-sc2723", "sprd,vbc-v4-codec-sc2730"
- sprd-audio-card,name : card name
- sprd-audio-card,widgets : simple widigets of the card
- sprd-audio-card,routing :
	A list of the connections between audio components.
	Each entry is a pair of strings, the first being the
	connection's sink, the second being the connection's
	source.
- sprd-audio-card,headset : reference node of sprd_headset

Dai-link subnode properties and subnodes:

Required dai-link subnodes:

- cpu					: CPU   sub-node
- codec					: CODEC sub-node
- plat					: PLATFORM sub-node

Required CPU/CODEC subnodes properties:
-sound-dai		: phandle/s and port of CPU/CODEC

Example:
sound_vbc_v4_sprd_codec: sound@0 {
	compatible = "sprd,vbc-v4-codec-sc2730";
	sprd-audio-card,name = "sprdphone-sc2730";
	sprd-audio-card,widgets =
		"Headphone", "inter HP PA",
		"Speaker", "inter Spk PA",
		"Speaker", "inter Ear PA";
	sprd-audio-card,routing =
		"HPMIC", "HPMIC Pin",
		"MIC", "MIC Pin",
		"AUXMIC", "MIC2 Pin",
		"inter HP PA", "HP Pin",
		"inter Spk PA", "SPK Pin",
		"inter Ear PA", "EAR Pin";
	sprd,ucp-smart-pa;
	sprd-audio-card,headset = <&sprd_headset>;
	sprd-audio-card,dai-link@0 {
		link-name = "FE_NORMAL_AP01";
		stream-name = "FE_ST_NORMAL_AP01";
		ignore-suspend = <0>;
		dynamic = <1>;
		trigger = <1 1>;
		dpcm-playback = <1>;
		dpcm-capture = <1>;
		be-id = <0>;
		plat {
			sound-dai = <&sprd_pcm>;
		};
		cpu {
			sound-dai = <&sprd_fe_dai 0>;
		};
		codec {
			sound-dai = <0 0>;
		};
	};
}
