[llvm] [LV] Prefer fixed VFs for epilogue vectorization (PR #211814)

[David Sherwood via llvm-commits]

https://github.com/david-arm approved this pull request.

LGTM. It might be good to also have a very simple test that defends the flag `scalable-epilogue-vf-cost-scale-factor`.

https://github.com/llvm/llvm-project/pull/211814