fdt: Introduce helper method fdt_overlay_apply_verbose()

Introduce fdt_overlay_apply_verbose, a method that applies an
overlay but in the case of an error produces a helpful message.

In addition if a base tree is found to be missing the __symbols__
node the message will point out that the probable reason is that
the base tree was miscompiled without the -@ option.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/fdt_support.h b/include/fdt_support.h
index 5ef78cc..2bca4d7 100644
--- a/include/fdt_support.h
+++ b/include/fdt_support.h
@@ -264,6 +264,8 @@
 int fdt_setup_simplefb_node(void *fdt, int node, u64 base_address, u32 width,
 			    u32 height, u32 stride, const char *format);
 
+int fdt_overlay_apply_verbose(void *fdt, void *fdto);
+
 #endif /* ifdef CONFIG_OF_LIBFDT */
 
 #ifdef USE_HOSTCC