dt-bindings: net: update Marvell PPv2 binding for PPv2.2 support

The Marvell PPv2 Device Tree binding was so far only used to describe
the PPv2.1 network controller, used in the Marvell Armada 375.

A new version of this IP block, PPv2.2 is used in the Marvell Armada
7K/8K processor. This commit extends the existing binding so that it can
also be used to describe PPv2.2 hardware.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>