ASoC: SOF: amd: refactor dmic codec platform device creation

Under snd_sof_dev device scope, create platform device for dmic
codec.

Signed-off-by: Vijendar Mukunda <Vijendar.Mukunda@amd.com>
Link: https://lore.kernel.org/r/168050621098.26.7486882101201297853@mailman-core.alsa-project.org


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