[llvm] [AMDGPU] Add amdgcn.av.global.(load|store).b128 intrinsics (PR #191390)

[Sameer Sahasrabuddhe via llvm-commits]

https://github.com/ssahasra commented:

#191389 needs to go in first so that the small globalisel change for metadata argument can be merged into this one.

https://github.com/llvm/llvm-project/pull/191390