media: ti-vpe: cal: Split media initialization and cleanup to functions

Create four functions to handle initialization, cleanup, registration
and unregistration of the V4L2 (and soon media controller) objects:

- init() is meant to be called early at probe time to initialize the
  objects, before they get used from within the kernel

- cleanup() is the counterpart of init, and is meant to be called at the
  end of the remove sequence to free all objects

- register() is meant to be called at the end of the probe sequence, to
  register the userspace-facing devices

- unregister() is the counterpart of register, and is meant to be called
  at the beginning for the remove sequence, to disallow access from
  userspace

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