linux/of.h: Add of_n_addr_cells()

Update #3277.

rtemsbsd/sys/powerpc/compat.c

@@ -204,6 +204,13 @@ get_size_cells(const void *fdt, int node)
 	return (get_cells(fdt, node, "#size-cells"));
 }
 
+int
+of_n_addr_cells(struct device_node *dn)
+{
+
+	return (get_address_cells(bsp_fdt_get(), dn->offset));
+}
+
 int
 of_address_to_resource(struct device_node *dn, int index,
     struct resource *res)