[WiP] Add buf_init_callbacks for dist inference = auto generate rope embeddings after meta/fake tracing
Author: lessw2020
Pull request: yes

add buf_init_callback.
This is an extension of the modeling_llama.py PR here: 
https://github.com/huggingface/transformers/pull/32428/files

# What does this PR do?
This adds the same class level buf_init_callback dict that allows someone to regenerate the rope embeddings that are destroyed during meta and then fake tracing.  (meta can be resolved via intercepting buffers, but running a fake tensor to trace for PP then destroys the rope embeddings as they become fake tensors. 

The buf_init_callbacks allows you to quickly find the entry point to regenerate all the non-persistent embeddings after tracing ensuring you have a ready to run model graph. 
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Comments:
cc @ArthurZucker @gante