media: ti-vpe: cal: Split video device initialization and registration

There's no need to delay most of the video device initialization until
the sensor subdevs are bound. Split the initialization and registration,
and perform the initialization when creating the context.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>