block: Make QUEUE_FLAG_x as an enum

This will allow us better keep in sync with blk_queue_flag_name[].

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20240719112912.3830443-8-john.g.garry@oracle.com


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