Merge pull request #5536 from mysterywolf/pm

[kernel][pm] beautify code

src/idle.c

@@ -241,7 +241,6 @@ static void rt_defunct_execute(void)
     }
 }
 
-extern void rt_system_power_manager(void);
 static void rt_thread_idle_entry(void *parameter)
 {
 #ifdef RT_USING_SMP
@@ -275,6 +274,7 @@ static void rt_thread_idle_entry(void *parameter)
 #endif /* RT_USING_SMP */
 
 #ifdef RT_USING_PM
+        void rt_system_power_manager(void);
         rt_system_power_manager();
 #endif /* RT_USING_PM */
     }