ASoC: rsnd: add TDM Split mode support

This patch adds TDM Split mode support. rsnd driver is assuming
audio-graph-scu-card is used for Sound Card.

This is very simple sample DT settings to use it.

	sound_card: sound {
		compatible = "audio-graph-scu-card";
		...
		convert-channels = <8>; /* TDM Split */

		dais = <&rsnd_port0     /* playback ch1/ch2 */
			&rsnd_port1     /* playback ch3/ch4 */
			&rsnd_port2     /* playback ch5/ch6 */
			&rsnd_port3     /* playback ch7/ch8 */
			>;
	};

	audio-codec {
		...
		port {
			codec_0: endpoint@1 {
				remote-endpoint = <&rsnd_ep0>;
			};
			codec_1: endpoint@2 {
				remote-endpoint = <&rsnd_ep1>;
			};
			codec_2: endpoint@3 {
				remote-endpoint = <&rsnd_ep2>;
			};
			codec_3: endpoint@4 {
				remote-endpoint = <&rsnd_ep3>;
			};
		};
	};

	&rcar_sound {
		...
		ports {
			rsnd_port0: port@0 {
				rsnd_ep0: endpoint {
					remote-endpoint = <&codec_0>;
					...
					playback = <&ssiu30 &ssi3>;
				};
			};
			rsnd_port1: port@1 {
				rsnd_ep1: endpoint {
					remote-endpoint = <&codec_1>;
					...
					playback = <&ssiu31 &ssi3>;
				};
			};
			rsnd_port2: port@2 {
				rsnd_ep2: endpoint {
					remote-endpoint = <&codec_2>;
					...
					playback = <&ssiu32 &ssi3>;
				};
			};
			rsnd_port3: port@3 {
				rsnd_ep3: endpoint {
					remote-endpoint = <&codec_3>;
					...
					playback = <&ssiu33 &ssi3>;
				};
			};
		};
	};

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>