[ALSA] hda-codec - Add suppoprt for Asus M2N-SLI motherboard

This patch adds a cfg_tbl to the ad1988 code with the Asus M2N-SLI as
it's first member.

Signed-off-by: Tobin Davis <tdavis@dsl-only.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>