arm64: dts: ls1088a: add DT node of watchdog

There are eight cores in ls1088a and each core has an watchdog,
ls1088a can use sp805-wdt driver, so we just add DT node for it.

Signed-off-by: Zhang Ying-22455 <ying.zhang22455@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>