[llvm] [mlir] Add usub_cond and usub_sat operations to atomicrmw (PR #105553)

[Matt Arsenault via llvm-commits]

arsenm wrote:

The AMDGPU change should be a separate PR entirely. Splitting the patches in one PR is of minimal help since they will be squashed on submit anyway 

https://github.com/llvm/llvm-project/pull/105553