Improve _update_causal_mask performance
Author: alessandropalla
Pull request: yes

# What does this PR do?

Fixes # (issue)
https://github.com/huggingface/transformers/issues/29206

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#create-a-pull-request),
      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.
- [ ] 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?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@ArthurZucker


Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_29210). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

@ArthurZucker I think it can be merged, if I found additional optimizations I'll add them into another PR

So, just ran locally `tests/models/[gemma,llama]/test_modeling_[gemma,llama].py` and got a bunch of errors that I'm not sure are related to the PR but most probably from my environment
```bash
FAILED tests/models/gemma/test_modeling_gemma.py::GemmaModelTest::test_cpu_offload - AssertionError: Items in the second set but not the first:
FAILED tests/models/gemma/test_modeling_gemma.py::GemmaModelTest::test_disk_offload_bin - ValueError: You are trying to offload the whole model to the disk. Please use the `disk_offload` function instead.
FAILED tests/models/gemma/test_modeling_gemma.py::GemmaModelTest::test_disk_offload_safetensors - ValueError: You are trying to offload the whole model to the disk. Please use the `disk_offload` function instead.
FAILED tests/models/gemma/test_modeling_gemma.py::GemmaModelTest::test_model_parallelism - AssertionError: Items in the second set but not the first:

FAILED tests/models/llama/test_modeling_llama.py::LlamaModelTest::test_cpu_offload - AssertionError: Items in the second set but not the first:
FAILED tests/models/llama/test_modeling_llama.py::LlamaModelTest::test_disk_offload_bin - ValueError: You are trying to offload the whole model to the disk. Please use the `disk_offload` function instead.
FAILED tests/models/llama/test_modeling_llama.py::LlamaModelTest::test_disk_offload_safetensors - ValueError: You are trying to offload the whole model to the disk. Please use the `disk_offload` function instead.
FAILED tests/models/llama/test_modeling_llama.py::LlamaModelTest::test_model_parallelism - AssertionError: Items in the second set but not the first:
```

In my env, `set(new_model.hf_device_map.values())` returns only `{cpu}`, also the other error seems to be `device_map` related

Yes those are unrelated! 

Thanks for the PR 🤗