[llvm] AMDGPU: Expand shuffle testing with generated tests (PR #123574)

[Shilei Tian via llvm-commits]

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

> Not sure if it's worth posting anywhere.

Probably somewhere like `llvm-project/llvm/utils/Target/AMDGPU`?

https://github.com/llvm/llvm-project/pull/123574