[media] cx23885: Cleanup MPEG encoder GPIO handling

During initialization the prior GPIO's were not being preserved
and restore correctly. Small cleanups to configure the GPIO's
for the HVR1700, HVR1800 and HVR1850.

Signed-off-by: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>