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/VideoBackendBase.cpp

@@ -93,7 +93,7 @@ std::string VideoBackendBase::BadShaderFilename(const char* shader_stage, int co
 void VideoBackendBase::Video_ExitLoop()
 {
   auto& system = Core::System::GetInstance();
-  system.GetFifo().ExitGpuLoop(system);
+  system.GetFifo().ExitGpuLoop();
 }
 
 // Run from the CPU thread (from VideoInterface.cpp)
@@ -379,7 +379,7 @@ bool VideoBackendBase::InitializeShared(std::unique_ptr<AbstractGfx> gfx,
   auto& system = Core::System::GetInstance();
   auto& command_processor = system.GetCommandProcessor();
   command_processor.Init(system);
-  system.GetFifo().Init(system);
+  system.GetFifo().Init();
   system.GetPixelEngine().Init(system);
   BPInit();
   VertexLoaderManager::Init();