alarmtimers: Remove period from alarm structure

Now that periodic alarmtimers are managed by the handler function,
remove the period value from the alarm structure and let the handlers
manage the interval on their own.

CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

include/linux/posix-timers.h

@@ -81,7 +81,10 @@ struct k_itimer {
 			unsigned long incr;
 			unsigned long expires;
 		} mmtimer;
-		struct alarm alarmtimer;
+		struct {
+			struct alarm alarmtimer;
+			ktime_t interval;
+		} alarm;
 		struct rcu_head rcu;
 	} it;
 };