[llvm] [NVPTX] Add syncscope support for cmpxchg (PR #140812)

[Akshay Deodhar via llvm-commits]

akshayrdeodhar wrote:

Also, I'm planning to make the fix to AtomicExpandPass for the [issue ](https://github.com/llvm/llvm-project/pull/140812#issuecomment-2923540205)that @gonzalobg pointed out in a separate PR: 

https://github.com/llvm/llvm-project/pull/140812