board: ls1088aqds: 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>