VideoCommon/Fifo: Pass system instance through FifoManager constructor

Given how many member functions make use of the system instance,
it's likely just better to pass the system instance in on construction.

Makes the interface a little less noisy to use.

Source/Core/VideoCommon/VideoConfig.cpp

@@ -67,13 +67,13 @@ void VideoConfig::Refresh()
 
       const bool lock_gpu_thread = Core::IsRunningAndStarted();
       if (lock_gpu_thread)
-        system.GetFifo().PauseAndLock(system, true, false);
+        system.GetFifo().PauseAndLock(true, false);
 
       g_Config.Refresh();
       g_Config.VerifyValidity();
 
       if (lock_gpu_thread)
-        system.GetFifo().PauseAndLock(system, false, true);
+        system.GetFifo().PauseAndLock(false, true);
     });
     s_has_registered_callback = true;
   }