ALSA: hdspm - Enable AD/DA/PH gains and S/PDIF-Input select on AIO

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: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>