Convert CONFIG_MII et al to Kconfig

This converts the following to Kconfig:
   CONFIG_MII
   CONFIG_DRIVER_TI_EMAC

Signed-off-by: Adam Ford <aford173@gmail.com>
Acked-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/sksimx6_defconfig b/configs/sksimx6_defconfig
index d695d47..bd9cc73 100644
--- a/configs/sksimx6_defconfig
+++ b/configs/sksimx6_defconfig
@@ -36,7 +36,7 @@
 CONFIG_PHY_MICREL=y
 CONFIG_PHY_MICREL_KSZ90X1=y
 CONFIG_PHY_MICREL_KSZ8XXX=y
-CONFIG_NETDEVICES=y
 CONFIG_FEC_MXC=y
+CONFIG_MII=y
 CONFIG_DM_THERMAL=y
 CONFIG_OF_LIBFDT=y