[media] em28xx: add support for em25xx/em276x/em277x/em278x frame data processing

The em25xx/em276x/em277x/em278x frame data format is different to the one used
by the em2710/em2750/em28xx chips.
With the recent cleanups and reorganization of the frame data processing code it
can be easily extended to support these devices.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>