[ALSA] hda: add dig mic support for sigmatel codecs

Adds support for digital microphone pin widgets on SigmaTel codecs.
Enables support only on the 9205 codecs for now.

Signed-off-by: Matt Porter <mporter@embeddedalley.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>