block: Enforce power-of-2 physical block size

The merging/splitting code and other queue limits checking depends on the
physical block size being a power-of-2, so enforce it.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20250729091448.1691334-3-john.g.garry@oracle.com


[axboe: add missing braces]
Signed-off-by: Jens Axboe <axboe@kernel.dk>