dm: Provide a way to shut down driver model

Add a new method which removes and unbinds all drivers.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Marek Vasut <marex@denx.de>
diff --git a/include/dm/root.h b/include/dm/root.h
index a4826a6..35818b1 100644
--- a/include/dm/root.h
+++ b/include/dm/root.h
@@ -50,4 +50,12 @@
  */
 int dm_init(void);
 
+/**
+ * dm_uninit - Uninitialise Driver Model structures
+ *
+ * All devices will be removed and unbound
+ * @return 0 if OK, -ve on error
+ */
+int dm_uninit(void);
+
 #endif