Revert "arm64: dts: ls1028a: sl28: get MAC addresses from VPD"

With commit b203e6f1 ("arm64: dts: ls1028a: sl28: get MAC addresses
from VPD"), the network adapter now depends on the nvmem device to be
present, which isn't the case and thus breaks networking on this board.
Revert it.

Fixes: b203e6f1

 ("arm64: dts: ls1028a: sl28: get MAC addresses from VPD")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>