[ALSA] Enable DXS controls for VIA VT82xx

Modules: VIA82xx driver

The patch enable separate DXS controls of sound function of VIA VT82xx
controller in case DXS volume is not needed for PCM Playback volume
control emulation.

Signed-off-by: Honza Maly <hkmaly@matfyz.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>