[llvm] AMDGPU: Drop and upgrade llvm.amdgcn.atomic.csub/cond.sub to atomicrmw (PR #105553)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Can you add some IR tests in test/Transforms/AtomicExpand? Need the 32/64 cases tested, and later I'll need to add the no fine grained memory vs. not cases 

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