[POWERPC] Add for_each_child_of_node() helper for iterating over child nodes

Add for_each_child_of_node() to encapsulate the common idiom of
iterating over the children of a device_node.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/linux/of.h

@@ -46,6 +46,10 @@ extern struct device_node *of_find_node_by_phandle(phandle handle);
 extern struct device_node *of_get_parent(const struct device_node *node);
 extern struct device_node *of_get_next_child(const struct device_node *node,
 					     struct device_node *prev);
+#define for_each_child_of_node(parent, child) \
+	for (child = of_get_next_child(parent, NULL); child != NULL; \
+	     child = of_get_next_child(parent, child))
+
 extern struct property *of_find_property(const struct device_node *np,
 					 const char *name,
 					 int *lenp);