Add UNPLUG traces to all appropriate places

Added blk_unplug interface, allowing all invocations of unplugs to result
in a generated blktrace UNPLUG.

Signed-off-by: Alan D. Brunelle <Alan.Brunelle@hp.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index c111105..f8e5917 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -35,8 +35,7 @@
 	for (i=0; i<mddev->raid_disks; i++) {
 		struct request_queue *r_queue = bdev_get_queue(devlist[i]->bdev);
 
-		if (r_queue->unplug_fn)
-			r_queue->unplug_fn(r_queue);
+		blk_unplug(r_queue);
 	}
 }