rtc: m41t80: use IRQ flags obtained from fwnode

Allow the IRQ type to be passed from the device tree if available as there
may be components changing the trigger type of the interrupt between the
RTC and the IRQ controller.

Link: https://lore.kernel.org/r/20230123200217.1236011-4-alexandre.belloni@bootlin.com


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