sed-opal: add support flag for SUM in status ioctl

Not every OPAL drive supports SUM (Single User Mode), so report this
information to userspace via the get-status ioctl so that we can adjust
the formatting options accordingly.
Tested on a kingston drive (which supports it) and a samsung one
(which does not).

Signed-off-by: Luca Boccassi <bluca@debian.org>
Link: https://lore.kernel.org/r/20230210010612.28729-1-luca.boccassi@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>