tick: export nohz tick idle symbols for module use

Allow drivers such as intel_powerclamp to use these apis for
turning on/off ticks during idle.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

kernel/time/tick-sched.c

@@ -553,6 +553,7 @@ void tick_nohz_idle_enter(void)
 
 	local_irq_enable();
 }
+EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
 
 /**
  * tick_nohz_irq_exit - update next tick event from interrupt exit
@@ -681,6 +682,7 @@ void tick_nohz_idle_exit(void)
 
 	local_irq_enable();
 }
+EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
 
 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
 {