AMDGPU: Increase vcc liveness scan threshold

Avoids a test regression in a future patch. Also add debug printing on
this case, so I waste less time debugging folds in the future.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375367 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed