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/stv0991_defconfig b/configs/stv0991_defconfig
index cdbf279..500fd65 100644
--- a/configs/stv0991_defconfig
+++ b/configs/stv0991_defconfig
@@ -26,6 +26,6 @@
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_PHY_MICREL=y
-CONFIG_NETDEVICES=y
 CONFIG_ETH_DESIGNWARE=y
+CONFIG_MII=y
 CONFIG_CADENCE_QSPI=y