[media] pci: Add tw5864 driver

Support for boards based on Techwell TW5864 chip which provides
multichannel video & audio grabbing and encoding (H.264, MJPEG,
ADPCM G.726).

This submission implements only H.264 encoding of all channels at D1
resolution.

Thanks to Mark Thompson <sw@jkqxz.net> for help, and for contribution of
H.264 startcode emulation prevention code.

Signed-off-by: Andrey Utkin <andrey.utkin@corp.bluecherry.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>