drivers: rtc: update alarm_set_callback to return ENOTSUP

This commit addresses the issue related to the rtc.h API returning ENOSYS
for a driver not implementing alarm_set_callback when the ALARM
functionality is enabled but interrupts, and thus alarm callbacks, are not
supported by the current configuration.

The following drivers have been modified to return correct code:
- rtc_pcf8523
- rtc_pcf8563
- rtc_rv3028

Signed-off-by: Jakub Topic <jakub.topic@anitra.cz>