Fix a bug where the frame pointer would not be saved sometimes.  The problem is that VectorProcFrame lowering would update FP, but t
his was after PEI::insertCSRSpillsAndRestores had been called to save the registers. The fix is to set FP has used in VectorProcFrameLowering::processFunctionBeforeCalleeSavedScan.
Also remove VectorProcFrameLowering::spillCalleeSavedRegisters just do nothing. It was basically just a copy of the code in PrologueEpilogueInserter, so overriding it was unnecessary.