support for pytorch-directml
# 🚀 Feature request

I would like to be able to work with the available models and trainer classes when using pytorch-directml under WSL

## Motivation

importing relevant huggingface packages results in a message that pytorch could not be detected and as such the models would not be available. there is an importable torch module though, provided by the pytorch-directml package.

## Your contribution

I'm not sure how many changes would be required to make this work. If the features of the fork of pytorch are close to the newest release, it wouldn't be much, but I do know that the directml implementation for tensorflow is quite out of date. (using 1.15 instead of 2 or greater)

Hello! If you can provide a reproducible example, we're happy to take a look!

It's probably a matter of adding `pytorch-directml` to this part of the `file_utils.py` file:

https://github.com/huggingface/transformers/blob/558f8543ba3860c736a7a9a4176ac20f23f9d5a0/src/transformers/file_utils.py#L67-L77

Like it is done here for many TensorFlow flavors:

https://github.com/huggingface/transformers/blob/558f8543ba3860c736a7a9a4176ac20f23f9d5a0/src/transformers/file_utils.py#L80-L112<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>`pytorch-directml` replces `torch`
But `transformers` dont recognice/accept it  

https://pypi.org/project/pytorch-directml/
https://docs.microsoft.com/en-us/windows/ai/directml/dml-intro<|||||>is this already added? i would like to be able to run transformers with `pytorch-directml`