ASoC: codecs: Add sun8i-a33 binding documentation

Allwinner SUN8I audio codec

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On Sun8i-A33 SoCs, the audio is separated in different parts:

	  - A DAI driver. It uses the "sun4i-i2s" driver which is

	  documented here:

	  Documentation/devicetree/bindings/sound/sun4i-i2s.txt

	  - An analog part of the codec which is handled as PRCM registers.

	  See Documentation/devicetree/bindings/sound/sun8i-codec-analog.txt

	  - An digital part of the codec which is documented in this current

	  binding documentation.

	  - And finally, an audio card which links all the above components.

	  The simple-audio card will be used.

	  See Documentation/devicetree/bindings/sound/simple-card.txt

This bindings documentation exposes Sun8i codec (digital part).

Required properties:

- compatible: must be "allwinner,sun8i-a33-codec"

- reg: must contain the registers location and length

- interrupts: must contain the codec interrupt

- clocks: a list of phandle + clock-specifer pairs, one for each entry

  in clock-names.

- clock-names: should contain followings:

   - "bus": the parent APB clock for this controller

   - "mod": the parent module clock

Here is an example to add a sound card and the codec binding on sun8i SoCs that

are similar to A33 using simple-card:

	sound {

		compatible = "simple-audio-card";

		simple-audio-card,name = "sun8i-a33-audio";

		simple-audio-card,format = "i2s";

		simple-audio-card,frame-master = <&link_codec>;

		simple-audio-card,bitclock-master = <&link_codec>;

		simple-audio-card,mclk-fs = <512>;

		simple-audio-card,aux-devs = <&codec_analog>;

		simple-audio-card,routing =

				"Left DAC", "Digital Left DAC",

				"Right DAC", "Digital Right DAC";

		simple-audio-card,cpu {

			sound-dai = <&dai>;

		};

		link_codec: simple-audio-card,codec {

			sound-dai = <&codec>;

		};

	soc@01c00000 {

		[...]

		audio-codec@1c22e00 {

			#sound-dai-cells = <0>;

			compatible = "allwinner,sun8i-a33-codec";

			reg = <0x01c22e00 0x400>;

			interrupts = <GIC_SPI 29 IRQ_TYPE_LEVEL_HIGH>;

			clocks = <&ccu CLK_BUS_CODEC>, <&ccu CLK_AC_DIG>;

			clock-names = "bus", "mod";

		};

	};