ASoC: AMD: Use mixer control to switch between DMICs

Having mixer control to switch between DMICs prevents user to
initiate capture simultaneously on both the DMIcs.
Earlier 2 separate devices, one for each DMIC, gave an option of
using them simultaneously, which is not supported.

Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
Link: https://lore.kernel.org/r/20200530095519.24324-1-akshu.agrawal@amd.com


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