dt-bindings: watchdog: fsl-imx7ulp-wdt: Add 'fsl,ext-reset-output'

The wdog may generate wdog_any external reset if the int_en bit is
configured, so add a property for this purpose in dt-binding doc.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20231010081909.2899101-2-ping.bai@nxp.com


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