[PowerPC] Revert P9 scheduling model to incomplete

Partially revert a previous change from commit: https://llvm.org/svn/llvm-project/llvm/trunk@314026
The previous change caused regressions on Power 9.

llvm-svn: 314835

llvm/lib/Target/PowerPC/PPCScheduleP9.td

@@ -22,7 +22,7 @@ def P9Model : SchedMachineModel {
   // Try to make sure we have at least 10 dispatch groups in a loop.
   let LoopMicroOpBufferSize = 60;
 
-  let CompleteModel = 1;
+  let CompleteModel = 0;
 
   let UnsupportedFeatures = [HasQPX];