ALSA: hda/realtek - Add quirk for Mac Pro 5,1 machines

A user reported that setting model=imac24 used to allow sound to work on their
Mac Pro 5,1 machine.  Commit 5671087f "Move ALC885 macpro and imac24 models
to auto-parser" removed this model option.  All Mac machines are now explicitly
handled with a quirk and the auto-parser.  This adds a quirk for the device
found on the Mac Pro 5,1 machines.

This (partially) fixes https://bugzilla.redhat.com/show_bug.cgi?id=808559



[sorted the new entry in the ID number order by tiwai]

Reported-by: Gabriel Somlo <somlo@cmu.edu>
Signed-off-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>