media: vimc: Centralize subdev internal_ops initialization

Initialize the subdev internal_ops field in the vimc_ent_sd_register()
function. This handles the internal ops the same way as the subdev ops,
and prepares for moving to the V4L2 subdev active state API.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>