Remove RTC WKALM programming, notify DSME of the next non-boot event

**Remove RTC WKALM programming.** DSME handles RTC programming, including WKALM. DSME listens to the timed signal next_bootup_event and programs RTC wakeup alarms accordingly.

**Add timestamp of next non-boot event to DBUS signal next_bootup_event.** DSME needs to know two things about events:

1. The trigger time of the next event that requires the device to be booted, DSME programs the RTC WKALM accordingly.

2. The trigger time of the next event which does not require the device to be booted, DSME uses this information to calculate when the device can be suspended.

(1) is already covered by the implementation of the DBUS signal next_bootup_event. This change set adds support for (2): it introduces a second parameter to next_bootup_event, which is a timestamp of the next alarm that does not require that the device
is powered up, case (2).