ALSA: hda - Map 3stack-hp model (ALC888) for HP Educ.ar

Added model=3stack-hp for HP Educ.ar desktop machine (103c:2a72).

Signed-off-by: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
Signed-off-by: Takashi Iwai <tiwai@suse.de>