[llvm] [AArch64] Add lowering for fixed-vector bf16 masked gather/scatter. (PR #210273)

[Shanzhi Chen via llvm-commits]

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

LGTM.
nit: There's one typo in the commit message: `oeprations` should be `operations`. Feel free to fix it while merging.

https://github.com/llvm/llvm-project/pull/210273