Converting FastPitch to TensorRT engine.
I wanted to convert my TTS system with TensorRT, HifiGAN models weren't problematic at all, but I've been unable to get the TensorRT engine from Fastpitch models.

I've exported both the HifiGAN and FastPitch models to ONNX, thanks to _Exportable.export()_ method, but the FastPitch ones fail to even get parsed by the ONNX parser from TensorRT.

That's the error I get:
```
[03/22/2022-09:23:02] [TRT] [E] [shuffleNode.cpp::symbolicExecute::387] Error Code 4: Internal Error (Reshape_1126: IShuffleLayer applied to shape tensor must have 0 or 1 reshape dimensions: dimensions were [-1,2])
[03/22/2022-09:23:02] [TRT] [E] parsers/onnx/ModelImporter.cpp:780: While parsing node number 1137 [Pad -> "1682"]:
[03/22/2022-09:23:02] [TRT] [E] parsers/onnx/ModelImporter.cpp:781: --- Begin node ---
[03/22/2022-09:23:02] [TRT] [E] parsers/onnx/ModelImporter.cpp:782: input: "1655"
input: "1680"
input: "1681"
output: "1682"
name: "Pad_1137"
op_type: "Pad"
attribute {
  name: "mode"
  s: "constant"
  type: STRING
}

[03/22/2022-09:23:02] [TRT] [E] parsers/onnx/ModelImporter.cpp:783: --- End node ---
[03/22/2022-09:23:02] [TRT] [E] parsers/onnx/ModelImporter.cpp:785: ERROR: parsers/onnx/ModelImporter.cpp:179 In function parseGraph:
[6] Invalid Node - Pad_1137
[shuffleNode.cpp::symbolicExecute::387] Error Code 4: Internal Error (Reshape_1126: IShuffleLayer applied to shape tensor must have 0 or 1 reshape dimensions: dimensions were [-1,2])
In node 1137 (parseGraph): INVALID_NODE: Invalid Node - Pad_1137
[shuffleNode.cpp::symbolicExecute::387] Error Code 4: Internal Error (Reshape_1126: IShuffleLayer applied to shape tensor must have 0 or 1 reshape dimensions: dimensions were [-1,2])
```
So it clearly seems like the TensorRT can't handle that particular padding.
I've tried using different ONNX Opset versions (11, 12, 13), tried converting the models from INT64 to INT32 myself, since I suspected the problem might lie in the fact that TensorRT doesn't natively support INT64 and it was attempting to cast the model down to INT32 itself, but nothing seems to work. 

The machine I'm working on has **CUDA 11.4** which I can't change, so I'm using **TensorRT v.8.2.2.1**.


Has anyone been successful in using TensorRT with FastPitch models or are they just not compatible? So far it seems to be a problem specific to FastPitch only.

If someone succeeded, was there a need to change the model - e.g. the paddings? Or if it worked out of the box, what's NeMo/ONNX opset/TensorRT versions combination to use?