block: export blk_validate_limits

While block drivers do the validation as part of committing them to the
queue, users that use the limit outside of a block device context have
to validate the limits and fill in the calculated values as well.

So far btrfs is the only user of queue limits without a block device,
and it has gotten away with that more or less by accident.  But with
commit 559218d4 ("block: pre-calculate max_zone_append_sectors")
this became fatal for setups that have small max zone append size,
as it won't be limited now.

Export blk_validate_limits so that it can be called directly from btrfs.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20241113084541.34315-2-hch@lst.de


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