fdt: Add Python support for adding/removing nodes

Pull this support from these upstream commits:

   bfbfab0 pylibfdt: Add a means to add and delete notes
   9005f41 pylibfdt: Allow delprop() to return errors

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

scripts/dtc/pylibfdt/libfdt.i_shipped

@@ -628,28 +628,50 @@ class Fdt(FdtRo):
         return check_err(fdt_setprop(self._fdt, nodeoffset, prop_name,
                                      val, len(val)), quiet)
 
-    def delprop(self, nodeoffset, prop_name):
+    def delprop(self, nodeoffset, prop_name, quiet=()):
         """Delete a property from a node
 
         Args:
             nodeoffset: Node offset containing property to delete
             prop_name: Name of property to delete
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Error code, or 0 if OK
 
         Raises:
             FdtError if the property does not exist, or another error occurs
         """
-        return check_err(fdt_delprop(self._fdt, nodeoffset, prop_name))
+        return check_err(fdt_delprop(self._fdt, nodeoffset, prop_name), quiet)
+
+    def add_subnode(self, parentoffset, name, quiet=()):
+        """Add a new subnode to a node
 
-    def del_node(self, nodeoffset):
+        Args:
+            parentoffset: Parent offset to add the subnode to
+            name: Name of node to add
+
+        Returns:
+            offset of the node created, or negative error code on failure
+
+        Raises:
+            FdtError if there is not enough space, or another error occurs
+        """
+        return check_err(fdt_add_subnode(self._fdt, parentoffset, name), quiet)
+
+    def del_node(self, nodeoffset, quiet=()):
         """Delete a node
 
         Args:
-            nodeoffset: Node offset containing property to delete
+            nodeoffset: Offset of node to delete
+
+        Returns:
+            Error code, or 0 if OK
 
         Raises:
-            FdtError if the node does not exist, or another error occurs
+            FdtError if an error occurs
         """
-        return check_err(fdt_del_node(self._fdt, nodeoffset))
+        return check_err(fdt_del_node(self._fdt, nodeoffset), quiet)
 
 
 class Property(bytearray):