ALSA: ac97 - vt1618 7.1 Audio Support

1. Implement 7.1 Output for vt1618 codec.
2. Fix typos in comments from my previous 1617a patch.

Signed-off-by: John L. Utz III <john.utz@dmx.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>