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: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NShaun Tancheff <shaun.tancheff@seagate.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

include/linux/blk_types.h

@@ -163,9 +163,9 @@ enum rq_flag_bits {
 	__REQ_INTEGRITY,	/* I/O includes block integrity payload */
 	__REQ_FUA,		/* forced unit access */
 	__REQ_PREFLUSH,		/* request for cache flush */
+	__REQ_RAHEAD,		/* read ahead, can fail anytime */
 
 	/* bio only flags */
-	__REQ_RAHEAD,		/* read ahead, can fail anytime */
 	__REQ_THROTTLED,	/* This bio has already been subjected to
 				 * throttling rules. Don't do it again. */
 
@@ -205,7 +205,7 @@ enum rq_flag_bits {
 	(REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)
 #define REQ_COMMON_MASK \
 	(REQ_FAILFAST_MASK | REQ_SYNC | REQ_META | REQ_PRIO | REQ_NOIDLE | \
-	 REQ_PREFLUSH | REQ_FUA | REQ_INTEGRITY | REQ_NOMERGE)
+	 REQ_PREFLUSH | REQ_FUA | REQ_INTEGRITY | REQ_NOMERGE | REQ_RAHEAD)
 #define REQ_CLONE_MASK		REQ_COMMON_MASK
 
 /* This mask is used for both bio and request merge checking */