board: ls1088ardb: transition to DM_ETH

In case CONFIG_DM_ETH is enabled, no hardcoding is necessary for
DPAA2 Ethernet devices. Compile out any unnecessary setup when
CONFIG_DM_ETH is activated.
Also, force the PCI devices to be enumerated at probe time.

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