[ALSA] Adding support for ATI IXP450 HD Audio device support

Documentation,HDA Intel driver
This patch changes the Intel HD Audio device driver to include
the support of HD Audio device embedded in ATI south bridge
IXP450. Because the design of ATI chipset follows intel HD Audio
specification 1.0, the programming method is the same as that
of intel HD Audio device exception one minor change which requires
to enable snoop for DMA transport. There are 3 changes that have been
made to hda_intel.c file.
  1. Added device ID for ATI HD Audio device;
  2. Increase maximum CODEC supported to 4;
  3. Enable snoop during the driver initialization.

Signed-off-by: Frederick Li <fli@ati.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>