MLBEDSW-3771: Updated to TF 2.4 flatbuffer schema

Updated tflite loader and mappings from tensorflow 2.3 to tensorflow 2.4

Signed-off-by: Tim Hall <tim.hall@arm.com>
Change-Id: I55884000ee139baf639bb0377008e0534f72fe94
diff --git a/ethosu/vela/tflite_writer.py b/ethosu/vela/tflite_writer.py
index 82a063f..e190a74 100644
--- a/ethosu/vela/tflite_writer.py
+++ b/ethosu/vela/tflite_writer.py
@@ -193,6 +193,7 @@
             self.operator_code_map[op_type] = (idx, tf_code, opt_serializer)
 
         OperatorCode.OperatorCodeStart(builder)
+        OperatorCode.OperatorCodeAddDeprecatedBuiltinCode(builder, tf_code if tf_code < 127 else 127)
         OperatorCode.OperatorCodeAddBuiltinCode(builder, tf_code)
         if custom_code_offset is not None:
             OperatorCode.OperatorCodeAddCustomCode(builder, custom_code_offset)