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

[Piotr Sobczak via cfe-commits]

piotrAMD wrote:

The change LG - thanks for adding support for bf16.

Agreed that the intrinsics should match the builtins for consistency (now or in a follow-up commit).
These intrinsics were added for the upcoming generation - it should be fine to rename them at this stage.

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