media: hantro: Implement V4L2_CID_JPEG_ACTIVE_MARKER control

The Hantro JPEG encoder driver adds various segments to the JPEG header.
While it would be quite complicated to make these segments selectable
to userspace, given that the driver has to fill in various fields in
these segments, and also take care of alignment, it would be nice if
the driver could signal to userspace what segments are included.

Implement the V4L2_CID_JPEG_ACTIVE_MARKER control, and make it read
only so that it always returns the set of segments that the driver adds.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>