[llvm] AMDGPU: Set max supported div/rem size to 64 (PR #80669)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Probably should add tests with power of 2 constant tests since the pass specifically avoids handling them. I'm a bit uncomfortable relying on that type of optimization though 

https://github.com/llvm/llvm-project/pull/80669