When the kernel stops feeding the watchdog, inform the user that it is
about to timeout in X seconds.
The message looks like: watchdog: watchdog0: timeout in 15 seconds
This is helpful to warn the user that, most likely,
CONFIG_WATCHDOG_OPEN_TIMEOUT seconds have elapsed and the userspace hasn't
start feeding the watchdog.
Signed-off-by: Mathieu Othacehe <othacehe@xxxxxxx>