[media] vim2m: add create_bufs and prepare_buf support

Add support for the missing VIDIOC_CREATE_BUFS and VIDIOC_PREPARE_BUF
ioctls.

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