conf/ucm: bytcr-rt5651: Add digital mic support

Add a new ucm/codecs/rt5651/DigitalMic.conf snippet for digital mic support
and include this in the default non board-specific bytcr-rt5651.conf.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>