watchdog: imx2_wdg: notify wdog core to stop ping worker on suspend

Suspend routine disables wdog clk. Nevertheless, the watchdog subsystem
is not aware of that and can still try to ping wdog through
watchdog_ping_work. In order to prevent such condition and therefore
prevent from system hang (caused by the wdog register access issued
while the wdog clock is disabled) notify watchdog core that the ping
worker should be canceled during watchdog core suspend and restored
during resume.

Signed-off-by: Michal Koziel <michal.koziel@emlogic.no>
Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210618195033.3209598-3-grzegorz.jaszczyk@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>