Alarm: Add one more RTC alarm type for poweroff alarm.

Now we use type of RTC_WAKEUP for the poweroff alarm.
Actually lots of other applications also use this type.
But these applications never expect the device will
power on after it has been shut down. So we need to
add dedicated alarm type for the Deskclock or similar
applications.

Change-Id: I5df2465c46de8fe875d1581bdefe26021c8ffb33
alarm: add JNI interface for clearing alarm

Add the JNI for clearing cancelled alarm, otherwise kernel driver
would know nothing about the alarm status. E.g. power-off alarm
would not be really cleared in alarm driver even it is cancelled
in the apps/framework.

Change-Id: I1250b3778de8961ba2a89d8ea8fa29d729bbc4e8