[llvm] X86: implement lowerings for shuffles on `bf16` element type. (PR #76076)

[Phoebe Wang via llvm-commits]

https://github.com/phoebewang requested changes to this pull request.

> Do you prefer to take this over or teach me how/where to add tests for this?

What's the problem you want to solve here? From the code, I think `v16bf16` is well supported. And I tested some `v8bf16/v32bf16` cases and they can generate correct code too.
So I think they are also supported, just have difference in the code with FP16.
If you know some failure cases, you can add them as test cases.

https://github.com/llvm/llvm-project/pull/76076