arm: dts: ls1028a: disable enetc-2 by default

The enetc-2 port is used as DSA master (connected back-to-back to
mscc_felix_port4). Since the convention is to not enable ports in the
common SoC dtsi unless they are used on the board, then enable enetc-2
only when mscc_felix_port4 itself is enabled.

All existing device trees appear to adhere to this rule, so disable
enetc-2 in the SoC dtsi.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>