dtoc: Support deleting device tree properties

Add support for deleting a device tree property. With the fallback
implementation this uses fdtput. With libfdt it uses the API call and
updates the offsets afterwards.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/fdt.py b/tools/dtoc/fdt.py
index c0ce5af..f01c7b1 100644
--- a/tools/dtoc/fdt.py
+++ b/tools/dtoc/fdt.py
@@ -184,6 +184,16 @@
         """
         raise NotImplementedError()
 
+    def DeleteProp(self, prop_name):
+        """Delete a property of a node
+
+        This should be implemented by subclasses
+
+        Args:
+            prop_name: Name of the property to delete
+        """
+        raise NotImplementedError()
+
 class Fdt:
     """Provides simple access to a flat device tree blob.