[media] xc5000: drivers should specify chip revision rather than firmware

Specify chip revision at attach time rather than a firmware image.
This is a better way to ensure that the correct firmware is loaded
for the correct revision of the chip.

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