[media] mb86a20s: add support for serial streams

By comparing the traffic between Pixelview (cx23102-based and Kworld
(saa7134-based), the only difference is at register 0xd5. After some
tests, It seems that it is used to change mode between serial and parallel.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>