[llvm] [AMDGPU] Add legalization rules for atomicrmw max/min ops (PR #180502)

[Petar Avramovic via llvm-commits]

https://github.com/petar-avramovic approved this pull request.

In general .ll test coverage in enough, no need to also write mir tests for simple rules

https://github.com/llvm/llvm-project/pull/180502