[init][smp] have secondary init run in arch code up to threading, and complete in secondary thread

-move the per-cpu initialization of the gic and cortex-a9 timer into an init hook.
  This removes the hard coded call in arm/arch.c
-make sure the timer initialization happens in the pre-threading callback, in case
  a secondary init hook needs the timer.

top/main.c

@@ -170,7 +170,8 @@ void lk_secondary_cpu_entry(void)
 
 static int secondary_cpu_bootstrap2(void *arg)
 {
-	lk_init_level_all(LK_INIT_FLAG_SECONDARY_CPUS);
+	/* secondary cpu initialize from threading level up. 0 to threading was handled in arch */
+	lk_init_level(LK_INIT_FLAG_SECONDARY_CPUS, LK_INIT_LEVEL_THREADING, LK_INIT_LEVEL_LAST);
 
 	return 0;
 }