net: add higmacv300 Ethernet driver for HiSilicon platform

It adds the driver for HIGMACV300 Ethernet controller found on HiSilicon
SoCs like Hi3798CV200.  It's based on a downstream U-Boot driver, but
quite a lot of code gets rewritten and cleaned up to adopt driver model
and PHY API.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/Makefile b/drivers/net/Makefile
index 51be72b..8d02a37 100644
--- a/drivers/net/Makefile
+++ b/drivers/net/Makefile
@@ -76,3 +76,4 @@
 obj-y += ti/
 obj-$(CONFIG_MEDIATEK_ETH) += mtk_eth.o
 obj-y += mscc_eswitch/
+obj-$(CONFIG_HIGMACV300_ETH) += higmacv300.o