[WIP] Move X-MOD models to facebook organization
# What does this PR do?

As discussed in https://github.com/huggingface/transformers/pull/20939, the new models https://huggingface.co/jvamvas/xmod-base etc. should be moved to the [facebook](https://huggingface.co/facebook) organization.

This PR changes the hardcoded model names in the code.

Next steps:
- [ ] Someone please add me to the facebook org
- [ ] I move the models
- [ ] PR can be merged
- [ ] I leave the facebook org

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case. https://github.com/huggingface/transformers/pull/20939
- [x] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [x] Did you write any new necessary tests?


## Who can review?

@ArthurZucker

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