[llvm] [LLVM][CodeGen][SVE] Make bf16 fabs/fneg isel consistent with fp16. (PR #147543)

[David Sherwood via llvm-commits]

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

LGTM. Seems reasonable, and in fact the sve-merging-unary.ll cases seem to be an improvement anyway.

https://github.com/llvm/llvm-project/pull/147543