btrfs: move cond_wake_up functions out of ctree

The file ctree.h serves as a header for everything and has become quite
bloated. Split some helpers that are generic and create a new file that
should be the catch-all for code that's not btrfs-specific.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3517,26 +3517,4 @@ static inline int btrfs_is_testing(struct btrfs_fs_info *fs_info)
 }
 #endif
 
-static inline void cond_wake_up(struct wait_queue_head *wq)
-{
-	/*
-	 * This implies a full smp_mb barrier, see comments for
-	 * waitqueue_active why.
-	 */
-	if (wq_has_sleeper(wq))
-		wake_up(wq);
-}
-
-static inline void cond_wake_up_nomb(struct wait_queue_head *wq)
-{
-	/*
-	 * Special case for conditional wakeup where the barrier required for
-	 * waitqueue_active is implied by some of the preceding code. Eg. one
-	 * of such atomic operations (atomic_dec_and_return, ...), or a
-	 * unlock/lock sequence, etc.
-	 */
-	if (waitqueue_active(wq))
-		wake_up(wq);
-}
-
 #endif