Add flex attention flags and args to Llama on Habana

[kareemshaik80]

What does this PR do?

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[regisss]

@kareemshaik80 Can you provide a command to run so that we can test it?
Also, I suggest adding a test for it in https://github.com/huggingface/optimum-habana/blob/main/tests/test_text_generation_example.py

[astachowiczhabana]

This change is covered in: #2246