Fix torch version comparisons (helps with +cu*** or +cpu official builds)

[LSinev]

Comparisons like version.parse(torch.__version__) > version.parse("1.6")
are True for torch==1.6.0+cu101 or torch==1.6.0+cpu (which is not intended, I suppose).

So version.parse(version.parse(torch.__version__).base_version) comparisons are preferred (and used in pytorch_utils.py but not in other places).

What does this PR do?

• Updated all comparisons to failsafe (when used in copypasting inspiration) version.parse(version.parse(torch.__version__).base_version)
• added some often used patterns to pytorch_utils.py

Did not check if original version checks were eligible. Believe original authors just missed this version check caveat.
Only torch version check changed (not sure if other packages may be affected).

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

As it is touching many parts of code: @patrickvonplaten, @LysandreJik, @sgugger

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Amazing job, thanks a lot!
The tests were not properly triggered so launching them now. Will merge if all is green!

[patrickvonplaten]

Wow very cool @LSinev !