[llvm] [AMDGPU] Do not fold hidden_grid_dims load from reqd_work_group_size (PR #205866)

[Wooseok Lee via llvm-commits]

wooseoklee wrote:

@arsenm I am addressing this issue, https://github.com/SemiAnalysisAI/FuzzX/blob/master/amdgpu/known-miscompiles/m108-lowerkernattrs-grid-dims-folded-from-reqd-wgsize/NOTES.md. I noticed that you simplified them with this PR, https://github.com/llvm/llvm-project/pull/185610. I don't know the history, so I just created this PR. Let me know if there is any missing background that I am not aware of. 

https://github.com/llvm/llvm-project/pull/205866