ALSA: hda - Add support of dual-ADCs for Realtek ALC275

Some VAIO models with ALC275 have dual ADCs for both internal and external
mics, and the driver needs to switch one of them appropriately.
This patch adds a basic support for this functionality, dynamic switching
between two ADCs per jack plug state.

Signed-off-by: Takashi Iwai <tiwai@suse.de>