drivers: net: ldpaa: add DTS based probing support

When CONFIG_DM_ETH is enabled DPAA2 network interfaces will now probe
based on DTS nodes with the "fsl,qoriq-mc-dpmac" compatible.
In this case, transform the ldpaa_eth driver into a UCLASS_ETH driver
and reuse the _open()/_tx()/_stop() functions already inplemented.

For the moment, the ldpaa_eth driver will support both configurations:
with or without CONFIG_DM_ETH enabled. Any 'struct eth_device' occurrence
now has a matching 'struct udevice' made mutually exclusive based on the
state of CONFIG_DM_ETH.

Signed-off-by: Florin Laurentiu Chiculita <florinlaurentiu.chiculita@nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>