Support TensorRT 7 (newer than JetPack 4.3)

[Tiryoh]

What does this implement/fix?

• Fix TensorRT pre-trained model load error other than engine file build for jetbot.
  • error: [TensorRT] ERROR: INVALID_ARGUMENT: Can not find binding of given name
  • engine file for jetbot: http://jetbot.org/v0.4.3/examples/object_following.html
• Add/Use FlattenConcat lib (FlattenConcat_TRT) load function to avoid assertion error with Tensor RT Version < 7.
  • assertion error: [TensorRT] INTERNAL ERROR: Assertion failed: mConcatAxisID == 1 || mConcatAxisID == 2 || mConcatAxisID == 3
  • ref: https://github.com/jkjung-avt/tensorrt_demos/issues/87
• Add notebook to generate Tensor RT engine file from UFF file.
  • The engine file (v0.3 and v0.4) listed on the NVIDIA's tutorial is not compatible with Tensor RT 7. This notebook generates engine file for Tensor RT 7.
    • ref: https://github.com/NVIDIA-AI-IOT/jetbot/issues/375#issuecomment-803445929

Does this close any currently open issues?

No, but these are related issues.

• https://github.com/rt-net/jnm_jupyternotebook/issues/11
• https://github.com/NVIDIA-AI-IOT/jetbot/issues/430#issuecomment-828633641
• https://github.com/NVIDIA-AI-IOT/jetbot/issues/375#issuecomment-803445929

How has this been tested?

Tested notebook (object_following/live_demo.ipynb) on JetPack 4.5.1 with Jetson Nano 4GB (B01)

The image was set up using https://github.com/rt-net/jnmouse_utils/blob/6b97cc8db0f734587653f42ae43f01c366c97b04/setup-scripts/jnmouse-setup-jetpack-4-5-1.sh.

Any other comments?

• Updating https://github.com/rt-net/jnm_jupyternotebook/blob/master/jnmouse/tensorrt_model.py is required

Checklists

• [x] I have read the CONTRIBUTING guidelines.
• [x] I have checked to ensure there aren't other open Pull Requests for the same change.