watchdog: imx2_wdg: Alow ping on suspend

The i.MX watchdog cannot be disabled by software once it has been
enabled. This means that it can't be stopped before suspend.

For systems that enter low power mode this is fine, as the watchdog will
be automatically stopped by hardware in low power mode. Not all i.MX
platforms support low power mode in the mainline kernel. For example the
i.MX7D does not enter low power mode and so will be rebooted 2 minutes
after entering sleep states.

This patch introduces a device tree property "fsl,ping-during-suspend"
that can be used to enable ping on suspend support for these systems.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220127104739.312592-1-alistair@alistair23.me


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