Simulator: Add scaling API to adjust for slow simulators

The simulation engine had the ability to pause already and properly handled load spikes, however, it was not hardened against constant drift. This addition enables it to run at a constant slower-than-realtime rate successfully.

src/drivers/drv_hrt.h

@@ -186,6 +186,11 @@ __EXPORT extern	void	hrt_start_delay(void);
  */
 __EXPORT extern void	hrt_stop_delay(void);
 
+/**
+ * Stop to delay the HRT, but with an exact delta time.
+ */
+__EXPORT extern void	hrt_stop_delay_delta(hrt_abstime delta);
+
 #endif
 
 __END_DECLS