Add FP16 Support for SageMaker Model Parallel

(This PR is still pending some changes/fixes)
This PR adds support for SageMaker Model Parallel with FP16.

- To Enable fp16 with SMMP, user needs to add `fp16: True` to `SM_HP_MP_PARAMETERS`, when there's mismatch between `SM_HP_MP_PARAMETERS` and trainer args, a warning log would be printed and `SM_HP_MP_PARAMETERS` will be used as truth.
- Remove amp related stuff for SMMP as SMMP manages it's own half precision.
- Added `clip_master_grads` for grad clipping
- Some minor fixes


## 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?
- [ ] 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.
- [ ] 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).
- [ ] Did you write any new necessary tests?



_The documentation is not available anymore as the PR was closed or merged._<|||||>@philschmid Please review or suggest review, thanks!<|||||>Can you just run `make style` on your branch to fix the code quality issue? Thanks!