[ALSA] hda-codec - Fix support for sigmatel codecs that have 2 or more ADCs

1) Create seperate mixer controls for each ADC
2) Make number of substreams of capture PCM device be equal to
   number of ADCs

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>