ethernet: Add new driver for Marvell Armada 375 network unit

This commit adds a new network driver for the network controller in Marvell
Armada 375 SoC.

Given the controller is very different from the ones in the other Marvell
SoCs that use the mv643xx_eth (Kirkwood, Orion, Discovery) and mvneta
(Armada 370/38x/XP) drivers, a new driver is needed.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
[Ezequiel: coding style cleanup]
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>