V4L/DVB (11765): cx23885: Add generic functions for driving GPIO's

The GPIO's on the product can be in one of three places. To date we've
mainly used the GPIO's on the bridge itself, and once on the encoder.
Rather than having the complexity of multiple GPIO writes/reads from
isolated placed in the driver we'll route them through this function,
so we can make intelligent decisions about 1) Where the GPIO lives
and 2) Whether it conflicts (based on board) with some other function
to avoid bugs.

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