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.h

@@ -8,11 +8,15 @@
 
 namespace Tegra {
 namespace Engines {
-namespace MaxwellCompute {
 
-void WriteReg(u32 method, u32 value);
+class MaxwellCompute final {
+public:
+    MaxwellCompute() = default;
+    ~MaxwellCompute() = default;
 
-} // namespace MaxwellCompute
+    /// Write the value to the register identified by method.
+    void WriteReg(u32 method, u32 value);
+};
 
 } // namespace Engines
 } // namespace Tegra