When wakeup-source is set in the devicetree, set up the device for
using the output as interrupt instead of clock. This is similar to
how other RTC devices handle this.

This allows the clock chip to turn on the board when wired to do
so in hardware.
Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Link: https://lore.kernel.org/r/20230821072013.7072-1-mike.looijmans@topic.nlSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>