media: dt-bindings: coda: Add compatible for CodaHx4 on i.MX51

Add a compatible for the CodaHx4 VPU used on i.MX51.

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