media: dt-bindings: media: ti-vpe: Document VPE driver

Device Tree bindings for the Video Processing Engine (VPE).

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>