net: add hifemac_mdio MDIO bus driver for HiSilicon platform

It adds the driver for the internal MDIO bus of HIFEMAC Ethernet
controller.  It's based on the mainstream linux driver.

Signed-off-by: Yang Xiwen <forbidden405@outlook.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 62c4763..ebab4d9 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -912,6 +912,14 @@
 	  This driver supports HIFEMAC Ethernet controller found on
 	  HiSilicon SoCs.
 
+config HIFEMAC_MDIO
+	bool "HiSilicon Fast Ethernet Controller MDIO interface"
+	depends on DM_MDIO
+	select DM_CLK
+	help
+	  This driver supports the internal MDIO interface of HIFEMAC
+	  Ethernet controller.
+
 config HIGMACV300_ETH
 	bool "HiSilicon Gigabit Ethernet Controller"
 	select DM_RESET