nvme: Add pr_ops read_keys support

nvme: Add pr_ops read_keys support

This patch adds support for the pr_ops read_keys callout by calling the
NVMe Reservation Report helper, then parsing that info to get the
controller's registered keys. Because the callout is only used in the
kernel where the callers, like LIO, do not know about controller/host IDs,
the callout just returns the registered keys which is required by the SCSI
PR in READ KEYS command.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20230407200551.12660-12-michael.christie@oracle.com
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>