sched: Support adding timers to the start of timer_list

If sched_add_timer() is called on a timer that would make it the new
head of the list, then add it and signal the board code that the timer
should be rescheduled.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/simulator/main.c

@@ -74,17 +74,22 @@ timer_is_before(uint32_t time1, uint32_t time2)
     return (int32_t)(time1 - time2) < 0;
 }
 
-void
-timer_periodic(void)
-{
-}
-
 uint32_t
 timer_read_time(void)
 {
     return 0; // XXX
 }
 
+void
+timer_kick(void)
+{
+}
+
+void
+timer_periodic(void)
+{
+}
+
 
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  * Turn stdin/stdout into serial console