[llvm] [AMDGPU][TTI] Add target hook for the custom instruction uniformity (PR #137639)

[Pankaj Dwivedi via llvm-commits]

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PankajDwivedi-25 wrote:

Got it, you guys are saying instead of using those two, I should use the newly added one.  

https://github.com/llvm/llvm-project/pull/137639