* Spreadtrum cpu dai driver

This node models spreadtrum codec dai driver

Required properties:

- compatible : "sprd,sc2721-audio-codec", "sprd,sc27xx-audio-codec",
	       "sprd,sc2720-audio-codec", "sprd,sc27xx-audio-codec",
- reg : analog codec registor offset
- interrupts : irq num of analog codec
- sprd,syscon-pmu-apb : pmu apb node
- nvmem-cells : A phandle to the calibration cells provided by eFuse device.
- nvmem-cell-names : A name list of nvmem-cells.
- #sound-dai-cells : it used to select codec dai number,
	if equal 0 means use default dai 0, if equal 1,
	the cpu dai number is determined by the second parameter
	of sound-dai property.

Example:
sprd_audio_codec_ana: audio-codec@700 {
	compatible = "sprd,sc2721-audio-codec", "sprd,sc27xx-audio-codec";
	#sound-dai-cells = <1>;
	reg = <0x700>;
	interrupts = <6 IRQ_TYPE_NONE>;
	sprd,syscon-pmu-apb = <&pmu_regs>;
};


sprd-audio-card,dai-link@1 {
	...
	codec {
		sound-dai = <&sprd_codec 1>;
	};
	...
};
