ALSA: hda - Add extra chmap for 2.1 outputs on ASUS laptops

ASUS N56VZ and N76VZ laptops have a bass speaker but its output comes
only from the right channel.  This patch adds the extra chmap specific
to these models.

Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=846531


Signed-off-by: Takashi Iwai <tiwai@suse.de>