[media] v4l2: integrate support for VIDIOC_QUERY_EXT_CTRL

Add the v4l2 core plumbing for the new VIDIOC_QUERY_EXT_CTRL ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>