arm64: dts: ls1028a: sl28: add support for variant 2

Now that there is support for the Felix switch this variant can also be
added. It features two external ports ethernet ports which are connected
to the internal switch core. No direct connection to any of the enetc's
is supported.

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