ALSA: HDA patch_via.c: Second S/PDIF (HDMI) support

The VT1702 and VT1708S have a second S/PDIF output which is used to
connect to a HDMI transmitter.  This patch adds support for it.

Signed-off-by: Harald Welte <HaraldWelte@viatech.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>