[ALSA] maestro3: HP OmniBook HW volume button magic

Maestro3 driver
Some HP OmniBook laptops (500 and 6000 at least) require some GPIO magic
before the HW volume buttons work. This patch makes them work mostly.
Something is still missing to make them work perfectly. However I have been
unable to figure out what exactly.

Signed-off-by: Ville Syrjala <syrjala@sci.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>