message: Allow quantized stats to be used for new quant scheme.
  quantized_input_stats is required to set quant parameters
  for quantized inputs to a TFLite model. Currently, it is
  only allowed for uint8, but we need to enable it for
  int8 as well to support the new quantization scheme.
diff: @@ -345,7 +345,8 @@ def build_toco_convert_protos(input_tensors,
  input_array.data_type = util.convert_dtype_to_tflite_type(
  input_tensor.dtype)
  - if toco.inference_input_type == _types_pb2.QUANTIZED_UINT8:
  + if toco.inference_input_type in \
  + [_types_pb2.QUANTIZED_UINT8, _types_pb2.INT8]:
  if not quantized_input_stats:
  raise ValueError("std_dev and mean must be defined when "
  "inference_input_type is QUANTIZED_UINT8.")
  