block: refacto blkdev_issue_zeroout

Split out two well-defined helpers for hardware supported Write Zeroes
and manually writing zeroes using the Write command.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20240701165219.1571322-9-hch@lst.de


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