[clang] AMDGPU: Rename and add bf16 support for global_load_tr builtins (PR #86202)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> > I don't think intrinsics are meant for users. Builtins are the user-facing front. :-)
> 
> Depending on who you consider an user. Are folks writing MLIR generators users?

They're consumers of an unstable API, changing intrinsics is fine 

https://github.com/llvm/llvm-project/pull/86202