[llvm] [AArch64][CostModel] Add SVE bfloat arithmetic tests (NFC) (PR #166951)

[David Green via llvm-commits]

https://github.com/davemgreen approved this pull request.

Thanks - this has worked quite well for FP16, hopefully it can work well here too.

LGTM

https://github.com/llvm/llvm-project/pull/166951