rtc: bd70528: Initial support for ROHM bd70528 RTC

Support RTC block in ROHM bd70528 power management IC. Support
getting and setting the time and date as well as arming an alarm
which can also be used to wake the PMIC from standby state.

HW supports wake interrupt only for the next 24 hours (sec, minute
and hour information only) so we limit also the alarm interrupt to
this 24 hours for the sake of consistency.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>