muorb: abs time on aDSP in sync with Linux side

This adds a call on startup of the muorb on the aDSP side to use an
offset for hrt_absolute_call(). This means that the hrt_absolute_call()
on the appsproc (Linux) side should now match the one on the aDSP
(QURT) side.
The accuracy still needs to be determined.

src/drivers/drv_hrt.h

@@ -109,6 +109,15 @@ __EXPORT extern hrt_abstime hrt_elapsed_time(const volatile hrt_abstime *then);
  */
 __EXPORT extern hrt_abstime hrt_store_absolute_time(volatile hrt_abstime *now);
 
+#ifdef __PX4_QURT
+/**
+ * Set a time offset to hrt_absolute_time on the DSP.
+ * @param time_diff_us: time difference of the DSP clock to Linux clock.
+ *   This param is positive because the Linux clock is ahead of the DSP one.
+ */
+__EXPORT extern int hrt_set_absolute_time_offset(int32_t time_diff_us);
+#endif
+
 /**
  * Call callout(arg) after delay has elapsed.
  *