ASoC: mediatek: add documents for mt6797

Mediatek AFE PCM controller for mt6797

Required properties:

- compatible = "mediatek,mt6797-audio";

- reg: register location and size

- interrupts: should contain AFE interrupt

- power-domains: should define the power domain

- clocks: Must contain an entry for each entry in clock-names

- clock-names: should have these clock names:

		"infra_sys_audio_clk",

		"infra_sys_audio_26m",

		"mtkaif_26m_clk",

		"top_mux_audio",

		"top_mux_aud_intbus",

		"top_sys_pll3_d4",

		"top_sys_pll1_d4",

		"top_clk26m_clk";

Example:

	afe: mt6797-afe-pcm@11220000  {

		compatible = "mediatek,mt6797-audio";

		reg = <0 0x11220000 0 0x1000>;

		interrupts = <GIC_SPI 151 IRQ_TYPE_LEVEL_LOW>;

		power-domains = <&scpsys MT6797_POWER_DOMAIN_AUDIO>;

		clocks = <&infrasys CLK_INFRA_AUDIO>,

			 <&infrasys CLK_INFRA_AUDIO_26M>,

			 <&infrasys CLK_INFRA_AUDIO_26M_PAD_TOP>,

			 <&topckgen CLK_TOP_MUX_AUDIO>,

			 <&topckgen CLK_TOP_MUX_AUD_INTBUS>,

			 <&topckgen CLK_TOP_SYSPLL3_D4>,

			 <&topckgen CLK_TOP_SYSPLL1_D4>,

			 <&clk26m>;

		clock-names = "infra_sys_audio_clk",

			      "infra_sys_audio_26m",

			      "mtkaif_26m_clk",

			      "top_mux_audio",

			      "top_mux_aud_intbus",

			      "top_sys_pll3_d4",

			      "top_sys_pll1_d4",

			      "top_clk26m_clk";

	};

MT6797 with MT6351 CODEC

Required properties:

- compatible: "mediatek,mt6797-mt6351-sound"

- mediatek,platform: the phandle of MT6797 ASoC platform

- mediatek,audio-codec: the phandles of MT6351 codec

Example:

	sound {

		compatible = "mediatek,mt6797-mt6351-sound";

		mediatek,audio-codec = <&mt6351_snd>;

		mediatek,platform = <&afe>;

	};