[llvm] [AMDGPU][Attributor] Infer `inreg` attribute in `AMDGPUAttributor` (PR #101609)

[Sameer Sahasrabuddhe via llvm-commits]

https://github.com/ssahasra commented:

Looks okay to me, with a few small fixes. But I am not familiar with all the implications of ``inreg``. Please wait for approval from @arsenm.

https://github.com/llvm/llvm-project/pull/101609