media: dt: bindings: Add binding for NVIDIA Tegra Video Decoder Engine

Add binding documentation for the Video Decoder Engine which is found
on NVIDIA Tegra20/30/114/124/132 SoC's.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-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>