rtc: tps6594: Add power management support

Add power management support to the driver. This allows a SoC to wake
from suspend using the nINT provided by the RTC.
It takes care of the case when the interrupt has not been caught because
the kernel has not yet woke up.
(This is the case when only edges interrupt are caught)

Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Link: https://lore.kernel.org/r/20240618141851.1810000-4-richard.genoud@bootlin.com


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