media: coda: Add i.MX51 (CodaHx4) support

Add support for the CodaHx4 VPU used on i.MX51.

Decoding h.264, MPEG-4, and MPEG-2 video works, as well as encoding
h.264. MPEG-4 encoding is not enabled, it currently produces visual
artifacts.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
[hans.verkuil@cisco.com: fix (bogus) sparse warning about uninited me_bits]
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>