ASoC: audio-graph: remove Platform support

ASoC: audio-graph: remove Platform support

Platform was one of mandatory component on ASoC before,
and audio-graph-card was assuming that CPU and Platform were
same driver.

But it is no longer mandatory on ASoC.
Current ASoC will just ignore if Platform and CPU were same
or doplicated component.

Of course ASoC is supporting Platform, but current
audio-graph-card doesn't support detecting it from DT.

This means current audio-graph-card operation for Platform so far
is 100% useless. This patch removes it.
We can respawn it when we need it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87sg3n3ubg.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>