Add a check to import_utils.py to allow for use of faiss_gpu installation
Author: Fiona-Waters
Pull request: yes

# What does this PR do?
When using Transformers RagRetriever and Milvus in a jupyter notebook, the faiss library is required. I specifically need faiss-gpu, but as the check for this is not implemented here I am unable to run my code. 
This PR adds a check for faiss-gpu to the existing faiss and faiss-cpu checks. 
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Fixes # (issue)
Related to https://github.com/huggingface/transformers/issues/11720 - previously closed

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