driver: net: ti: introduce common mdio support library

All existing TI SoCs network HW have similar MDIO implementation, so
introduce common mdio support library which can be reused by TI networking
drivers.

Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/ti/Makefile b/drivers/net/ti/Makefile
index 4ab4a27..d2b6f20 100644
--- a/drivers/net/ti/Makefile
+++ b/drivers/net/ti/Makefile
@@ -2,6 +2,6 @@
 #
 # Copyright (C) 2018 Texas Instruments Incorporated - http://www.ti.com/
 
-obj-$(CONFIG_DRIVER_TI_CPSW) += cpsw.o cpsw-common.o
+obj-$(CONFIG_DRIVER_TI_CPSW) += cpsw.o cpsw-common.o cpsw_mdio.o
 obj-$(CONFIG_DRIVER_TI_EMAC) += davinci_emac.o
 obj-$(CONFIG_DRIVER_TI_KEYSTONE_NET) += keystone_net.o