Add file locking hooks

Does nothing so far, but adds locking calls that cover from ->prep()
to after ->queue(). That is the period where we do IO.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/filesetup.c b/filesetup.c
index 483226a..188b0ce 100644
--- a/filesetup.c
+++ b/filesetup.c
@@ -645,6 +645,14 @@
 	return ret;
 }
 
+void lock_file(struct thread_data *td, struct fio_file *f)
+{
+}
+
+void unlock_file(struct fio_file *f)
+{
+}
+
 static int recurse_dir(struct thread_data *td, const char *dirname)
 {
 	struct dirent *dir;