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/video_core/engines/maxwell_compute.cpp

@@ -6,10 +6,8 @@
 
 namespace Tegra {
 namespace Engines {
-namespace MaxwellCompute {
 
-void WriteReg(u32 method, u32 value) {}
+void MaxwellCompute::WriteReg(u32 method, u32 value) {}
 
-} // namespace MaxwellCompute
 } // namespace Engines
 } // namespace Tegra