net: Add support for Broadcom GENETv5 Ethernet controller

net: Add support for Broadcom GENETv5 Ethernet controller

The Broadcom GENET Ethernet MACs are used in several MIPS based SoCs
and in the Broadcom 2711/2838 SoC used on the Raspberry Pi 4.
There is no publicly available documentation, so this driver is based
on the Linux driver. Compared to that the queue management is
drastically simplified, also we only support version 5 of the IP and
RGMII connections between MAC and PHY, as used on the RPi4.

Signed-off-by: Amit Singh Tomar <amittomer25@gmail.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
[Andre: heavy cleanup and a few fixes]
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>