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

[via llvm-commits]

anjenner wrote:

Just to keep you updated, I now have a patch which splits off the AMDGPU CodeGen parts of this patch and all tests are passing. I have a few more bits of testcase work to do as a result of review feedback. I'll create a PR for that on Monday. Once that lands, I'll rebase this PR on top of that one and this will just be the "drop and upgrade" parts.

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