System: Implement CPU overclocking [SAVEVERSION+]

Partial credit to @CookiePLMonster as well.

src/core/memory_card.h

@@ -35,7 +35,6 @@ private:
   {
     // save in three seconds, that should be long enough for everything to finish writing
     SAVE_DELAY_IN_SECONDS = 5,
-    SAVE_DELAY_IN_SYSCLK_TICKS = MASTER_CLOCK * SAVE_DELAY_IN_SECONDS,
   };
 
   union FLAG
@@ -74,6 +73,8 @@ private:
     WriteEnd,
   };
 
+  static TickCount GetSaveDelayInTicks();
+
   bool LoadFromFile();
   bool SaveIfChanged(bool display_osd_message);
   void QueueFileSave();