[llvm] [AMDGPU] Remove definition of hi16 for scalar registers (PR #197467)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

> This seems debatable. I don't know the original purpose to have the sgpr lo16 defined. From true16 perspective, we could end up want to support sgpr_lo16 in the pipeline (also debatable) so we have a dedicate sreg assigned for 16bit types.

I think in this case we will want to have both lo16 and hi16.

https://github.com/llvm/llvm-project/pull/197467