Update the PP2 ethernet ports subnodes' names to match
schema enforced by the marvell,pp2.yaml contents.

Add new required properties ('reg') which contains information
about the port ID, keeping 'port-id' ones for backward
compatibility.
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>