ARM: Add a mechanism for faking CPU time elapsed during HLE.

- Also a few cleanups.

src/core/arm/interpreter/arm_interpreter.h

@@ -60,6 +60,12 @@ public:
      */
     u64 GetTicks() const override;
 
+    /**
+    * Advance the CPU core by the specified number of ticks (e.g. to simulate CPU execution time)
+    * @param ticks Number of ticks to advance the CPU core
+    */
+    void AddTicks(u64 ticks) override;
+
     /**
      * Saves the current CPU context
      * @param ctx Thread context to save