cpuload: Support the internal computation in the tickless mode

just like how the same thing done in nxsched_process_timer

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

sched/sched/sched_timerexpiration.c

@@ -385,6 +385,19 @@ static unsigned int nxsched_timer_process(unsigned int ticks,
   clock_update_wall_time();
 #endif
 
+#if defined(CONFIG_SCHED_CPULOAD) && !defined(CONFIG_SCHED_CPULOAD_EXTCLK)
+  /* Perform CPU load measurements (before any timer-initiated context
+   * switches can occur)
+   */
+
+#ifdef CONFIG_HAVE_WEAKFUNCTIONS
+  if (nxsched_process_cpuload_ticks != NULL)
+#endif
+    {
+      nxsched_process_cpuload_ticks(ticks);
+    }
+#endif
+
   /* Process watchdogs */
 
   tmp = nxsched_process_wdtimer(ticks, noswitches);