Fifo: Extract syncing loop

It's now a new helper function within common.

Source/Core/VideoCommon/Fifo.h

@@ -43,6 +43,7 @@ void* PopFifoAuxBuffer(size_t size);
 
 void FlushGpu();
 void RunGpu();
+void GpuMaySleep();
 void RunGpuLoop();
 void ExitGpuLoop();
 void EmulatorState(bool running);