GPU: Move the GPU's class constructor and destructors to a cpp file.

This should reduce recompile times when editing the Maxwell3D register structure.

src/video_core/gpu.cpp

@@ -0,0 +1,21 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "video_core/engines/fermi_2d.h"
+#include "video_core/engines/maxwell_3d.h"
+#include "video_core/engines/maxwell_compute.h"
+#include "video_core/gpu.h"
+
+namespace Tegra {
+
+GPU::GPU() {
+    memory_manager = std::make_unique<MemoryManager>();
+    maxwell_3d = std::make_unique<Engines::Maxwell3D>(*memory_manager);
+    fermi_2d = std::make_unique<Engines::Fermi2D>();
+    maxwell_compute = std::make_unique<Engines::MaxwellCompute>();
+}
+
+GPU::~GPU() = default;
+
+} // namespace Tegra