Expose the namespace metadata format when PI is enabled. The user needs
to enable the capability per subsystem and per port. The other metadata
properties are taken from the namespace/bdev.

Usage example:
echo 1 > /config/nvmet/subsystems/${NAME}/attr_pi_enable
echo 1 > /config/nvmet/ports/${PORT_NUM}/param_pi_enable
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>