ALSA: hda: Input port AMP controls

Added support for controlling hardware gain amps on input ports
using a volume control mixer with a mux selecting the port being controlled.

Signed-off-by: Matthew Ranostay <mranostay@embeddedalley.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>