block: sed-opal: Introduce Opal Datastore UID

This patch introduces Opal Datastore UID.
The generic read/write table ioctl can use this UID
to access the Opal Datastore.

Reviewed-by: Scott Bauer <sbauer@plzdonthack.me>
Reviewed-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Revanth Rajashekar <revanth.rajashekar@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>