drivers: net: fsl-mc: add support for CONFIG_DM_ETH

Make any adjustments necessary in order to support DPAA2 devices probed
using CONFIG_DM_ETH. While at it, fixup some styling issues aroung the
switch-case statement.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>