rtc: pm8xxx: Attach wake irq to device

Attach the interrupt as a wake-irq to the device, so that:
- A corresponding wakeup source is created (and reported in e.g
  /sys/kernel/debug/wakeup_sources).
- The power subsystem take cares of arming/disarming
  irq-wake automatically on suspend/resume.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1645025082-6138-1-git-send-email-loic.poulain@linaro.org