block: move read-only and supported checks into (__)blkdev_issue_zeroout

Move these checks out of the lower level helpers and into the higher level
ones to prepare for refactoring.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240701165219.1571322-8-hch@lst.de


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