[RAG] fix generate
# What does this PR do?

#9984 introduced a new `encoder_no_repeat_ngram_size`  `generate` param, but it was missing from `RagTokenForGeneration.generate`,  it's a required argument for `_get_logits_processor` which is called inside `RagTokenForGeneration.generate`.

This PR adds the argument to `RagTokenForGeneration.generate` and passes it to `_get_logits_processor`.
Wow this is a huge bug actually! Thanks a lot for fixing it @patil-suraj! 

@LysandreJik @sgugger - Sadly Circle CI is skipping all RAG tests at the moment -> therefore we should first fix the faiss import (#10103), then rebase this PR to see that everything is correctly solved, merge it and then do a patch 