[Executorch][llama] Rename update_quantized_cache to update_cache

Pull Request resolved: https://github.com/pytorch/executorch/pull/6914

Because it is just really an inplace update op. Nothing special
ghstack-source-id: 255730819
@exported-using-ghexport

Differential Revision: [D66041160](https://our.internmc.facebook.com/intern/diff/D66041160/)

Co-authored-by: Kimish Patel <kimishpatel@fb.com>