ALSA: ymfpci - Don't create invalid PCM & mixers when AC97 doesn't support

- check SDAC bit of AC97 primary codec when create "rear" device 3,
  "4ch" device 2 and "4ch Duplication" switch as the card need a four channels
  AC97 codec to support surround40.

Signed-off-by: Raymond Yau <superquad.vortex2@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>