arm64: dts: ls1028a: use phy-mode instead of phy-connection-type

In linux both are identical, phy-mode is used more often, though. Also
for the ls1028a both phy-connection-type and phy-mode was used, one for
the enetc nodes and the other for the switch nodes. Unify them. But the
main reason for this is that the device tree files can be shared with
the u-boot ones; there the enetc driver only supports the "phy-mode"
property.

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>