[llvm] [AMDGPU] Extend zero initialization of return values for TFE (PR #85759)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> There's no global isel support implemented yet - but I thought that could maybe be a separate change? (I'm not sure about the best approach currently).

I think it's best to do them together, otherwise they bifurcate 

https://github.com/llvm/llvm-project/pull/85759