rtc: rx8111: handle VLOW flag

Allow userspace to get battery status information and be able to warn when
battery is low and has to be replaced.

Tested-by: Waqar Hameed <waqar.hameed@axis.com>
Reviewed-by: Waqar Hameed <waqar.hameed@axis.com>
Link: https://lore.kernel.org/r/20240417191937.33790-2-alexandre.belloni@bootlin.com


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