net: Add MT7628 ethernet driver

This patch adds ethernet support for the MIPS based Mediatek MT76xx SoCs
(e.g. MT7628 and MT7688), including a minimum setup of the integrated
switch. This driver is loosly based on the driver version included in
this MediaTek github repository:

https://github.com/MediaTek-Labs/linkit-smart-uboot.git

Tested on the MT7688 LinkIt smart-gateway and on the
Gardena-smart-gateway.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Frank Wunderlich <frankwu@gmx.de>
Cc: Weijie Gao <hackpascal@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 3968743..3ce46c8 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -227,6 +227,13 @@
 	  The Cadence MACB ethernet interface was used on Zynq platform.
 	  Say Y to enable support for the MACB/GEM in Zynq chip.
 
+config MT7628_ETH
+	bool "MediaTek MT7628 Ethernet Interface"
+	depends on ARCH_MT7620
+	help
+	  The MediaTek MT7628 ethernet interface is used on MT7628 and
+	  MT7688 based boards.
+
 config PCH_GBE
 	bool "Intel Platform Controller Hub EG20T GMAC driver"
 	depends on DM_ETH && DM_PCI