ASoC: tas5720: add basic support for TAS5722 devices

The TI TAS5722 digital amplifier is very similar to the TAS5720 from an
overall and register map perspective. Therefore the existing driver can be
extended easily to support this additional device. This commit allows
TAS5722 devices to be used in a "subset" type of fashion, without exposing
any of the additional features they offer.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>