net: ethernet: mediatek: Add MT7628/88 SoC support

This patch adds support for the MediaTek MT7628/88 SoCs to the common
MediaTek ethernet driver. Some minor changes are needed for this and
a bigger change, as the MT7628 does not support QDMA (only PDMA).

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: René van Dorst <opensource@vdorst.com>
Cc: Daniel Golle <daniel@makrotopia.org>
Cc: Sean Wang <sean.wang@mediatek.com>
Cc: John Crispin <john@phrozen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>