ASoC: simple-card-utils: share dummy DAI and reduce memory

Current simple-card / audio-graph creates 1xCPU + 1xCodec + 1xPlatform
for all dai_link, but some of them is not needed.
For example Platform is not needed for DPCM BE case.
Moreover, we can share snd-soc-dummy DAI for CPU-dummy / dummy-Codec
in DPCM.

This patch adds dummy DAI and share it when DPCM case,
I beliave it can contribute to reduce memory.

By this patch, CPU-dummy / dummy-CPU are set at asoc_simple_init_priv(),
thus, its settings are no longer needed at DPCM detecting timing
on simple-card / audio-graph.
Moreover, we can remove triky Platform settings code for DPCM BE,
because un-needed Platform is not created.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87tuoqod22.wl-kuninori.morimoto.gx@renesas.com


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