drivers: watchdog: wdt_mcux_wwdt: Add PM support for low power modes

Enables sleep mode (PM3) on RW61x. The driver
re-enables the wdt on wake-up based on the previous
configuration. Note that the wdt counter value always
resets to the max window value on wake-up

Signed-off-by: Alex Rodriguez <alejandro.rodriguezlimon@nxp.com>