This patch uses the newly introduced HDSPM_CONTROL_TRISTATE functions to
create and expose the following ALSA controls:

   - Gain selection for Input, Output and Phones (HiGain, +4dBu, -10dbV)
   - S/PDIF Input select (Coaxial, Optical, Internal)
Signed-off-by: NAdrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>