ARM: pxa: hx4700: use gpio descriptors for audio

The audio driver should not use a hardwired gpio number
from the header. Change it to use a lookup table.

Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Paul Parsons <lost.distance@yahoo.com>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: alsa-devel@alsa-project.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>