[ALSA] HDA - enable snoop on SCH

This patch enables snoop on Intel SCH chipset, eliminating static during
playback.

Signed-off-by: Tobin Davis <tdavis@dsl-only.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>