scsi: target: iblock: Allow iblock devices to be shared

scsi: target: iblock: Allow iblock devices to be shared

We might be running a local application that also interacts with the
backing device. In this setup we have some clustering type of software
that manages the ownwer of it, so we don't want the kernel to restrict
us. This patch allows the user to control if the driver gets exclusive
access.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20250721185145.20913-1-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>