[media] cx231xx: add support for Hauppauge EXETER

Add support for various Hauppauge EXETER designs.

Note by DJH: fixed a few minor 'make checkpatch' warnings before commit.

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