Phi3FlashAttention2 call to rotary embeddings bugfix
Author: alaskar-10r
Pull request: yes

# What does this PR do?
The Phi3RotaryEmbedding forward call (all of its implementations) requires position_ids as an input arg but in the Phi3FlashAttention2 implementation it is called with just the seq_len argument. I'm adding position_ids back (looks like they were removed here: https://github.com/huggingface/transformers/pull/31500) and also adding a check for either position_ids or seq_len to exist in the forward call, and using seq_len to define the position_ids when only the seq_len was provided. Cascading those changes to other places where this code is used.

@ArthurZucker 

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Comments:
cc @gante too 

➕ for this. Phi3+FA2 is broken in the latest transformers release