[llvm] AMDGPU: Make bf16/v2bf16 legal types (PR #76215)

[Pierre van Houtryve via llvm-commits]

https://github.com/Pierre-vh commented:

Test changes are a bit hard to review so I didn't look at all of them

Do we need a GISel equivalent of this patch?

https://github.com/llvm/llvm-project/pull/76215