dm: core: Add ofnode_read_resource()

We sometimes need to read a resource from an arbitrary node. In any case
for consistency we should not put the live-tree switching code in
a dev_read_...() function. Update this to suit.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Beaver, Jetson-TK1
Tested-by: Stephen Warren <swarren@nvidia.com>

include/dm/ofnode.h

@@ -15,6 +15,8 @@
 /* Enable checks to protect against invalid calls */
 #undef OF_CHECKS
 
+struct resource;
+
 /**
  * ofnode - reference to a device tree node
  *
@@ -605,4 +607,6 @@ int ofnode_read_simple_size_cells(ofnode node);
  */
 bool ofnode_pre_reloc(ofnode node);
 
+int ofnode_read_resource(ofnode node, uint index, struct resource *res);
+
 #endif