Fix case when using --gradient_accumulation_steps with DDP disabled.
Author: sangeethabal
Pull request: yes

# What does this PR do?
When --gradient_accumulation_steps option is used with DDP disabled, HF has a call to ```model.no_sync``` which doesn't exist. This PR is to fix the issue of ```model.no_sync```
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Fixes # (issue)
https://github.com/aws-neuron/aws-neuron-sdk/issues/635

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## Who can review?
@sgugger 


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

> I think it would be easier to just adapt [this property](https://github.com/huggingface/transformers/blob/dfe9a3197364c7f0e2169d7c16c357c9c1311cb9/src/transformers/training_args.py#L1802) to add the torch_neuroncore_available there.

@sgugger I have made the required changes to this PR itself. Please take a look. TIA