arm64: dts: s32g399a-rdb3: Enable the SWT watchdog

The SWT0 is directly connected to the reset line and only one instance
is useful for its purpose. Let's enable it on the s32g399a-rdb3.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Ghennadi Procopciuc <ghennadi.procopciuc@nxp.com>
Cc: Thomas Fossati <thomas.fossati@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>