media: vim2m: use workqueue

v4l2_ctrl uses mutexes, so we can't setup a ctrl_handler in
interrupt context. Switch to a workqueue instead and drop the timer.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>