[llvm] [AMDGPU] CodeGen for GFX12 VBUFFER instructions (PR #75492)

[Piotr Sobczak via llvm-commits]

piotrAMD wrote:

We may need to also update the following files with gfx12 run lines (can be a separate patch):
* test/CodeGen/AMDGPU/llvm.amdgcn.raw.tbuffer.load.d16.ll
* test/CodeGen/AMDGPU/llvm.amdgcn.struct.buffer.load.format.v3f16.ll
* test/CodeGen/AMDGPU/llvm.amdgcn.struct.tbuffer.load.d16.ll

https://github.com/llvm/llvm-project/pull/75492