[llvm] AMDGPU: Assume true in getVOPNIsSingle helpers (PR #98516)

[Joe Nash via llvm-commits]

https://github.com/Sisyph commented:

I don't think we should be relying on the default behavior. So wouldn't it make sense to mark your instructions of interest as isCodeGenOnly = 0, if they are actually getting printed? Or set IsSingle on them?
If we don't need a bit in TSFlags, it's better to not use it imo.

https://github.com/llvm/llvm-project/pull/98516