arm64: dts: imx8mq-evk: enable watchdog

The external nWDOG signal connects to the EVK board reset circuit.

Tested on the i.MX8MQ EVK rev B3.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>