update kvcache mistral

[skaulintel]

What does this PR do?

Fixes # (issue)

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• 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?

[bgoldberg-habana]

if we use the same class of kv cache in all models (llama,mistral/ falcon), let's move it to modeling_all_models and use it from there

[skaulintel]

if we use the same class of kv cache in all models (llama,mistral/ falcon), let's move it to modeling_all_models and use it from there

@bgoldberg-habana I moved KVCache class to modeling_all_models.py. I want this PR to focus on mistral specifically. Will open a separate PR for consolidating all models using KVCache.

see #148 for all other models

[astachowiczhabana]

huggingface#918