rtc: rv8803: add wakeup-source support

The RV8803 can be wired directly to a PMIC that can wake up an SoC without
the CPU getting interrupts.

Link: https://lore.kernel.org/r/20240108004357.602918-1-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>