ALSA: snd-aoa: Add a layout entry for PowerBook6,5

Either one or a combination of commits 81e5d864
"Register i2c devices from device-tree" and 3a3dd018
"Improve detection of devices from device-tree" broke sound on
PowerBook6,5 machines.

Fix it by adding an entry to the new driver to match PowerBook6,5
machines.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>