[dsmetool] Added --clear-rtc parameter to dsmetool

This will clear alarm from RTC.
This implementation works only when dsme is not running.
Later we might want to add functionality also to support running dsme but now this is intended to be used during preinit when dsme is not running.

Signed-off-by: Pekka Lundstrom <pekka.lundstrom@jollamobile.com>