arm64: dts: ls1028: sl28: explicitly enable network ports

arm64: dts: ls1028: sl28: explicitly enable network ports

Since commit b9213899d2b0 ("arm64: dts: ls1028a: disable all enetc ports
by default") all the network ports are disabled by default. This makes
sense, but now we have to enable them explicitly in the boards. Do so
for the sl28 module.

Since we are at it. Make sure the second port is only enabled for the
variant 4 of the module. Variant 3 has only one network port.

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