rtc: add AB-RTCMC-32.768kHz-EOZ9 RTC support

This patch adds support for AB-RTCMC-32.768kHz-EOZ9 RTC/Calendar
module with I2C interface.

Signed-off-by: Artem Panfilov <panfilov.artyom@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>