arm64: dts: imx8mm: Reinstate GPIO watchdog always-running property on eDM SBC

The GPIO watchdog property name is 'always-running', not 'always-enabled'.
Use the correct property name and reinstate it into the DT.

Fixes: eff6b33c ("arm64: dts: imx8mm: Remove watchdog always-enabled property from eDM SBC")
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>