[media] coda: copy headers in front of every I-frame

That way we don't have to rely on userspace to inject the headers on IDR
requests, and there is always enough information to start decoding at an
I-frame.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>