ASoC: audio-graph-card2: add DPCM support

This patch adds DPCM support to audio-graph-card2.
It uses "dpcm" node (= D), needs to have routing (= A),
need to indicate both FE/BE at links (= B, C).
dpcm ports@0 is for FE (= B), port@1 is for BE (= C).
remote-endpoint can use both Single/Multi connection.

			DSP
		  ************
	PCM0 <--> * fe0  be0 * <--> DAI0: Codec Headset
	PCM1 <--> * fe1  be1 * <--> DAI1: Codec Speakers
	PCM2 <--> * fe2  be2 * <--> DAI2: MODEM
	PCM3 <--> * fe3  be3 * <--> DAI3: BT
		  *	 be4 * <--> DAI4: DMIC
		  *	 be5 * <--> DAI5: FM
		  ************

	sound {
		compatible = "audio-graph-card2";

		// indicate routing
(A)		routing = "xxx Playback", "xxx Playback",
			  "xxx Playback", "xxx Playback",
			  "xxx Playback", "xxx Playback";

		// indicate all Front-End, Back-End in DPCM case
(B)		links = <&fe0, &fe1, ...
(C)			 &be0, &be1, ...

(D)		dpcm {
			// Front-End
			ports@0 {
(B)				fe0: port@0 { fe0_ep: endpoint { remote-endpoint = <&pcm0_ep>; }; };
(B)				fe1: port@1 { fe1_ep: endpoint { remote-endpoint = <&pcm1_ep>; }; };
				...
			};
			// Back-End
			ports@1 {
(C)				be0: port@0 { be0_ep: endpoint { remote-endpoint = <&dai0_ep>; }; };
(C)				be1: port@1 { be1_ep: endpoint { remote-endpoint = <&dai1_ep>; }; };
				...
			};
		};
	};

	CPU {
		ports {
			bitclock-master;
			frame-master;
			port@0 { pcm0_ep: endpoint { remote-endpoint = <&fe0_ep>; }; };
			port@1 { pcm1_ep: endpoint { remote-endpoint = <&fe1_ep>; }; };
			...
		};
	};

	Codec {
		ports {
			port@0 { dai0_ep: endpoint { remote-endpoint = <&be0_ep>; }; };
			port@1 { dai1_ep: endpoint { remote-endpoint = <&be1_ep>; }; };
			...
		};
	};

Link: https://lore.kernel.org/r/87k0xszlep.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87zgrelu4v.wl-kuninori.morimoto.gx@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>