media: coda: pad first buffer with repeated MPEG headers to fix sequence init

If the first buffer contains only headers, the sequence initialization
command fails. On CodaHx4 the buffer must be padded to at least 512
bytes, on CODA960 it seems to be enough to just repeat the sequence and
extension headers (MPEG-2) or the VOS and VO headers (MPEG-4) once for
for sequence initialization to succeed without further bitstream data.
On CodaHx4 the headers can be repeated multiple times until the 512 byte
mark is reached.

A similar issue was solved for h.264 by padding with a filler NAL in
commit 0eef8940 ("[media] coda: pad first h.264 buffer to 512
bytes").

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>