dm: core: Add a way to convert a devicetree to a dtb

Add a way to flatten a devicetree into binary form. For livetree this
involves generating the devicetree using fdt_property() and other calls.
For flattree it simply involves providing the buffer containing the tree.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/core/ofnode.c

@@ -243,6 +243,24 @@ int oftree_new(oftree *treep)
 
 #endif /* OFNODE_MULTI_TREE */
 
+int oftree_to_fdt(oftree tree, struct abuf *buf)
+{
+	int ret;
+
+	if (of_live_active()) {
+		ret = of_live_flatten(ofnode_to_np(oftree_root(tree)), buf);
+		if (ret)
+			return log_msg_ret("flt", ret);
+	} else {
+		void *fdt = oftree_lookup_fdt(tree);
+
+		abuf_init(buf);
+		abuf_set(buf, fdt, fdt_totalsize(fdt));
+	}
+
+	return 0;
+}
+
 /**
  * ofnode_from_tree_offset() - get an ofnode from a tree offset (flat tree)
  *