ALSA: snd-aoa: handle older machines

This patch changes snd-aoa to handle some older machines that are
currently handled by snd-powermac. snd-aoa has a number of advantages
though, notably it can autoload better and is generally a more modern
driver.

By hardcoding the accepted device-ids (last hunk of the patch) I'm
trying to avoid regressions because this driver will otherwise load
automatically and not let snd-powermac load. People who are unhappy
with snd-powermac and have a device-id property in the device tree
are encouraged to read this patch and make a patch to amend this as
appropriate.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>