libblkid: introduce luks opal prober

libblkid: introduce luks opal prober

Accesses to a disk locked with OPAL trigger IO errors logged by the
kernel which should be avoided.
Running the normal luks prober first breaks the ordering of probers
leading to incorrect detections, for example detecting mdadm superblocks
before version 1.1 as luks.

Introduce a new prober that only runs on OPAL-locked disks to avoid
these false-positives.

See #2061, #2373 and #2882.

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>