ALSA: hda: add more board-specific information for Realtek ALC662 rev1

I recently got a chance to play with two boards with ALC662 rev1:
* BIOSTAR TA780G M2+
* ASROCK K10N78FullHD-hSLI R3.0
Both use 3 stack, 6ch mode with digital out. Since autodetection isn't able
to figure that out from BIOS, we need to specify that manually.

Signed-off-by: Vedran Miletic <rivanvx@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>