docs: sysfs-block: Clarify integrity sysfs attributes

docs: sysfs-block: Clarify integrity sysfs attributes

The /sys/block/<disk>/integrity fields are historically set
if T10 protection Information is enabled.

It is not set if some upper layer uses integrity metadata.
Document it.

Signed-off-by: Milan Broz <gmazyland@gmail.com>
Co-developed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250318154447.370786-1-gmazyland@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>