drivers: rtc: Add Micro Crystal RV-8803-C7 RTC driver

This PR adds support for Micro Crystal RV-8803-C7
RTC chip.

Supported functionalities:
* Update interrupt
* Alarm interrupt
* Time setting/reading
* Alarm setting/reading
* Aging offset calibration setting/reading
* CLKOUT configuration

Tested on nRF52833-DK using rtc_api test set.

Signed-off-by: Marcin Lyda <elektromarcin@gmail.com>