ASoC: DMIC codec: Adding a generic DMIC codec

This codec is to be used by the DMIC driver to
control the DMIC codec.  This driver will be used on future
implementations of the DMIC driver to support codec specific
features.

At this time, the codec driver just registers the codec DAI.

Signed-off-by: David Lambert <dlambert@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>