block: Generalize chunk_sectors support as boundary support

The purpose of the chunk_sectors limit is to ensure that a mergeble request
fits within the boundary of the chunck_sector value.

Such a feature will be useful for other request_queue boundary limits, so
generalize the chunk_sectors merge code.

This idea was proposed by Hannes Reinecke.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20240620125359.2684798-3-john.g.garry@oracle.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>