ARM: imx: novena: Enable DM ethernet

Convert to DM ethernet to prevent board removal.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Vagrant Cascadian <vagrant@debian.org>