ASoC: meson: add axg tdm interface DT bindings documentation

* Amlogic Audio TDM Interfaces

Required properties:

- compatible: 'amlogic,axg-tdm-iface'

- clocks: list of clock phandle, one for each entry clock-names.

- clock-names: should contain the following:

  * "sclk" : bit clock.

  * "lrclk": sample clock

  * "mclk" : master clock

	     -> optional if the interface is in clock slave mode.

- #sound-dai-cells: must be 0.

Example of TDM_A on the A113 SoC:

tdmif_a: audio-controller@0 {

	compatible = "amlogic,axg-tdm-iface";

	#sound-dai-cells = <0>;

	clocks = <&clkc_audio AUD_CLKID_MST_A_MCLK>,

		 <&clkc_audio AUD_CLKID_MST_A_SCLK>,

		 <&clkc_audio AUD_CLKID_MST_A_LRCLK>;

	clock-names = "mclk", "sclk", "lrclk";

};