arm64: dts: ls1028a: mark enetc port 3 as a DSA master too

The LS1028A switch has 2 internal links to the ENETC controller.

With DSA's ability to support multiple CPU ports, we should mark both
ENETC ports as DSA masters.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>