block: move REQ_RAHEAD to common flags

The information that am I/O is a read-ahead can be useful for drivers.
In fact the NVMe driver already checks it, even if it won't ever be set
at the moment.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Shaun Tancheff <shaun.tancheff@seagate.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
1 file changed