Simplify ONNX Graph/ Compatibily GAP9 SDK

[pbonazzi]

I have just simplified the ONNX Graph
Some Hardware Accellerator (like GAP9) don't support Neg operations.

Referenced here:
#1555

[pbonazzi]

Basically instead of doing Neg + Add, I recommend using Sub

[BloodAxe]

Thanks for your contribution @pbonazzi ! Overall it looks good to be accepted.

However our policy requires all commits in PR should be signed.
Please follow https://github.com/Deci-AI/super-gradients/blob/master/CONTRIBUTING.md to setup PGP key and how to update existing PR with signed commits.
Once once we would be happy with accepting it.

[BloodAxe]

Superseded by #1584

[pbonazzi]

Thank you LGTM