core: Move PageTable struct into Common.

src/common/memory_hook.cpp

@@ -0,0 +1,11 @@
+// Copyright 2018 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "common/memory_hook.h"
+
+namespace Common {
+
+MemoryHook::~MemoryHook() = default;
+
+} // namespace Common