watchdog: pm8916_wdt: Add system sleep callbacks

Add suspend and resume pm operations.
Tested on dragonboard-410c.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1581435483-6796-1-git-send-email-loic.poulain@linaro.org


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>