[media] media: ti-vpe: Document CAL driver

Device Tree bindings for the Camera Adaptation Layer (CAL) driver

Signed-off-by: Benoit Parrot <bparrot@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>