block: Add bdev atomic write limits helpers

Add helpers to get atomic write limits for a bdev, so that we don't access
request_queue helpers outside the block layer.

We check if the bdev can actually atomic write in these helpers, so we
can avoid users missing using this check.

Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20241019125113.369994-4-john.g.garry@oracle.com


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