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

[Changpeng Fang via cfe-commits]

changpeng wrote:

> I don't think intrinsics are meant for users. Builtins are the user-facing front. :-)

Then renaing the intrinsics should be relatively at a lower priority. We may do it in a separate patch once we have reached an agreement.

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