[llvm] AMDGPU: Add codegen for atomicrmw operations usub_cond and usub_sat (PR #141068)

[via llvm-commits]

================
@@ -1,213 +0,0 @@
-; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
----------------
anjenner wrote:

I have restored it in the latest version of this patch.

https://github.com/llvm/llvm-project/pull/141068