block: add async version of bio_set_polled

If we know that a iocb is async we can optimise bio_set_polled() a bit,
add a new helper bio_set_polled_async().
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8fa137885164a5d05fadcff4c3521da8d5a83d00.1635337135.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/fops.c

@@ -358,14 +358,13 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
 		task_io_account_write(bio->bi_iter.bi_size);
 	}
 
-	if (iocb->ki_flags & IOCB_NOWAIT)
-		bio->bi_opf |= REQ_NOWAIT;
-
 	if (iocb->ki_flags & IOCB_HIPRI) {
-		bio_set_polled(bio, iocb);
+		bio->bi_opf |= REQ_POLLED | REQ_NOWAIT;
 		submit_bio(bio);
 		WRITE_ONCE(iocb->private, bio);
 	} else {
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			bio->bi_opf |= REQ_NOWAIT;
 		submit_bio(bio);
 	}
 	return -EIOCBQUEUED;