[PowerPC] [NFC] rename PPCLoopPreIncPrep.cpp to PPCLoopInstrFormPrep.cpp after D67088

[jsji]

Summary

This is NFC code clean work after D67088. In that patch, we extend loop instructions prep for ds/dq form.

This patch only changes the file name PPCLoopPreIncPrep.cpp to PPCLoopInstrFormPrep.cpp for better reviewing of the content change of file PPCLoopInstrFormPrep.cpp.

[shchenz]

LGTM

llvm/lib/Target/PowerPC/CMakeLists.txt

add_llvm_target(PowerPCCodeGen
   PPCCTRLoops.cpp
   PPCHazardRecognizers.cpp
   PPCInstrInfo.cpp
   PPCISelDAGToDAG.cpp
   PPCISelLowering.cpp
   PPCEarlyReturn.cpp
   PPCFastISel.cpp
   PPCFrameLowering.cpp
-  PPCLoopPreIncPrep.cpp
+  PPCLoopInstrFormPrep.cpp
   PPCMCInstLower.cpp
   PPCMachineFunctionInfo.cpp
   PPCMachineScheduler.cpp
   PPCMIPeephole.cpp
   PPCRegisterInfo.cpp
   PPCQPXLoadSplat.cpp
   PPCSubtarget.cpp
   PPCTargetMachine.cpp

llvm/utils/gn/secondary/llvm/lib/Target/PowerPC/BUILD.gn

sources = [
     "PPCEarlyReturn.cpp",
     "PPCExpandISEL.cpp",
     "PPCFastISel.cpp",
     "PPCFrameLowering.cpp",
     "PPCHazardRecognizers.cpp",
     "PPCISelDAGToDAG.cpp",
     "PPCISelLowering.cpp",
     "PPCInstrInfo.cpp",
-    "PPCLoopPreIncPrep.cpp",
+    "PPCLoopInstrFormPrep.cpp",
     "PPCLowerMASSVEntries.cpp",
     "PPCMCInstLower.cpp",
     "PPCMIPeephole.cpp",
     "PPCMachineFunctionInfo.cpp",
     "PPCMachineScheduler.cpp",
     "PPCPreEmitPeephole.cpp",
     "PPCQPXLoadSplat.cpp",
     "PPCReduceCRLogicals.cpp",