arm64: dts: ls1028a: sl28: expose switch ports in KBox A-230-LS

The KBox A-230-LS supports four external ports which are connected to
the internal switch of the LS1028A via QSGMII. Now that the Felix switch
is supported, add these ports in the device tree.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>