Make a GPU class in VideoCore to contain the GPU state.

Also moved the GPU MemoryManager class to video_core since it makes more sense for it to be there.

src/core/core.cpp

@@ -154,6 +154,8 @@ System::ResultStatus System::Init(EmuWindow* emu_window, u32 system_mode) {
         break;
     }
 
+    gpu_core = std::make_unique<Tegra::GPU>();
+
     telemetry_session = std::make_unique<Core::TelemetrySession>();
 
     CoreTiming::Init();