arm64: dts: ls1028a: move PHY nodes to MDIO controller

Move the PHY nodes from the network controller to the dedicated MDIO
controller. According to Vladimir Oltean direct MDIO access via the PF,
that is when the PHY is put under the "mdio" subnode, is defeatured and
in fact the latest reference manual isn't mentioning it anymore.

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