net: calxedagmac: Convert to DM_ETH

To squash that nasty warning message and make better use of the newly
gained OF_CONTROL feature, let's convert the calxedagmac driver to the
"new" driver model.
The conversion is pretty straight forward, mostly just adjusting the
use of the involved data structures.
The only actual change is the required split of the receive routine into
a receive and free_pkt part.
Also this allows us to get rid of the hardcoded platform information and
explicit init calls.

This also uses the opportunity to wrap the code decoding the MMIO
register base address, to make it safe for using PHYS_64BIT later.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>