[ALSA] hda - Add support for the ATI RS600 HDMI audio device

Add support for the ATI RS600 HDMI audio device. It has a one-stream
pure digital stereo codec that isn't handled by the generic codec
support.

Signed-off-by: Felix Kuehling <fkuehlin@ati.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>