ALSA: powermac - Allow input from microphone on Tumbler

Allow input from microphone on remaining PowerBooks and iBooks with Tumbler.
Tested only with PowerBook G4 Gigabit Ethernet (PowerBook3,3).

[Fixed to use of_machine_is_compatible by tiwai]

Signed-off-by: Risto Suominen <Risto.Suominen@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>