[clang] [llvm] AMDGPU: Add builtin/intrinsic global_(load|store)_b128 (PR #172090)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> @shiltian @arsenm: Are you ok with @ssahasra's suggestion:
> 
> > the Clang builtins should take a standard scope enum just like the scoped atomics, but the LLVM intrinsic can take a string literal and parse it in the same way as other scoped intrinsics.

Yes, I agree enums are better to work with 

https://github.com/llvm/llvm-project/pull/172090