AMDGPU: Rename intrinsics and remove f16/bf16 versions for load transpose (#86313)

Rename the intrinsics to close to the instruction mnemonic names:
Use global_load_tr_b64 and global_load_tr_b128 instead of
global_load_tr.

This patch also removes f16/bf16 versions of builtins/intrinsics. To
simplify the design, we should avoid enumerating all possible types in
implementing builtins. We can always use bitcast.