ASoC: simple-card: add comment to indicate don't remove platforms

ASoC: simple-card: add comment to indicate don't remove platforms

Basically CPU and Platform are different Component, but if CPU is using
soc-generic-dmaengine-pcm, same dev will be shared between CPU and
Platform, and Simple Card had been supporting it.

When we focus to clean up Simple Card driver, we tend to remove platforms
if no Platform was selected, but it is wrong because of above reasons.

This patch adds comment why we shouldn't remove platforms.

In case of CPU is not using soc-generic-dmaengine-pcm, CPU and Platform
will be duplicated, but it will be ignored by snd_soc_rtd_add_component().

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/875yattwqv.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>