arm64: dts: add big-endian property back into watchdog node

commit 720fd1cb upstream.

Watchdog doesn't work on NXP ls1046ardb board because in commit
7c8ffc55("arm64: dts: layerscape: remove big-endian for mmc nodes"),
it intended to remove the big-endian from mmc node, but the big-endian of
watchdog node is also removed by accident. So, add watchdog big-endian
property back.

In addition, add compatible string fsl,ls1046a-wdt, which allow big-endian
property.

Fixes: 7c8ffc55 ("arm64: dts: layerscape: remove big-endian for mmc nodes")
Cc: stable@vger.kernel.org
Signed-off-by: Meng Li <Meng.Li@windriver.com>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>