ALSA: cs5535 - Make OLPC-stuff depending on MGEODE_LX

The GPIO stuff for OLPC in cs5535audio_olpc.c is implemented only for
Geode-LX, and enabled only when CONFIG_MGEODE_LX=y.  Without this
config option, the driver gets build errors.

This patch adds a workaround to make it dependent on CONFIG_MGEODE_LX.

Ideally, the OLPC-GPIO stuff should be implemented in a way
independent from CPU type selection...

Signed-off-by: Takashi Iwai <tiwai@suse.de>