nvme: introduce max_integrity_segments ctrl attribute

This patch doesn't change any logic, and is needed as a preparation
for adding PI support for fabrics drivers that will use an extended
LBA format for metadata and will support more than 1 integrity segment.

Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>