[llvm] AMDGPU: Restore dropped EXEC/SCC defs on SI_KILL_F32_COND_IMM (PR #227604)

[Jay Foad via llvm-commits]

jayfoad wrote:

> With the defs gone, selection was free to leave a compare result in SCC
> across the kill. #134718 then marked SCC live-in to the split block to
> satisfy the verifier, which can probably cleaned up.

@mssefat can you follow up on this? Can/should #134718 be reverted now?

https://github.com/llvm/llvm-project/pull/227604