of: Add unit tests for applying overlays

Existing overlay unit tests examine individual pieces of the overlay
code.  The new tests target the entire process of applying an overlay.

Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/of_private.h

@@ -55,6 +55,18 @@ static inline int of_property_notify(int action, struct device_node *np,
 }
 #endif /* CONFIG_OF_DYNAMIC */
 
+#ifdef CONFIG_OF_UNITTEST
+extern void __init unittest_unflatten_overlay_base(void);
+#else
+static inline void unittest_unflatten_overlay_base(void) {};
+#endif
+
+extern void *__unflatten_device_tree(const void *blob,
+			      struct device_node *dad,
+			      struct device_node **mynodes,
+			      void *(*dt_alloc)(u64 size, u64 align),
+			      bool detached);
+
 /**
  * General utilities for working with live trees.
  *