V4L/DVB (9584): Support different GPIO/GPO registers for newer devices

Empia moved the location of the GPIO/GPO registers in newer devices.  Add the
ability to specify the relocated registers (including caching of register
contents).

Thanks for Ray Lu from Empia for providing the em2874 datasheet.

Signed-off-by: Devin Heitmueller <devin.heitmueller@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>