Introduce some basic H264 decoding support in cedrus. So far, only the
baseline profile videos have been tested, and some more advanced features
used in higher profiles are not even implemented.

Reviewed-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>