video_core: Remove usages of System::GetInstance() within the engines

Avoids the use of the global accessor in favor of explicitly making the
system a dependency within the interface.

src/core/core.cpp

@@ -128,7 +128,7 @@ struct System::Impl {
             return ResultStatus::ErrorVideoCore;
         }
 
-        gpu_core = std::make_unique<Tegra::GPU>(renderer->Rasterizer());
+        gpu_core = std::make_unique<Tegra::GPU>(system, renderer->Rasterizer());
 
         cpu_core_manager.Initialize(system);
         is_powered_on = true;