ASoC: audio-graph-card2-custom-sample.dtsi: add Codec2Codec sample (Single)

This patch adds Codec2Codec-Single sample to audio-graph-card2-custom-sample.dtsi.
Because it can use very basic connection only for now,
it can use only

	- 2channels
	- S32_LE format

Test-Component driver has "IN" and "OUT" widget. Thus the route is

	+--+
	|  | <-- Codec6 <-- IN
	|  | --> Codec7 --> OUT
	+--+

One note here is that it will start works when it boot.
In other words we can't stop it so far.
We need to update driver for it in the future.

	...
	asoc-audio-graph-card2-custom-sample: test_codec.7 <-> test_codec.6 mapping ok
	test-component test_codec: test_dai_startup() : test_codec.6
	test-component test_codec: test_dai_startup() : test_codec.7
	...

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87o87ulu2o.wl-kuninori.morimoto.gx@renesas.com


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