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/twister_defconfig b/configs/twister_defconfig
index b47c336..4e3000c 100644
--- a/configs/twister_defconfig
+++ b/configs/twister_defconfig
@@ -37,9 +37,10 @@
 CONFIG_NAND=y
 CONFIG_SYS_NAND_BUSWIDTH_16BIT=y
 CONFIG_SPL_NAND_SIMPLE=y
-CONFIG_NETDEVICES=y
+CONFIG_MII=y
 CONFIG_SMC911X=y
 CONFIG_SMC911X_BASE=0x2C000000
+CONFIG_DRIVER_TI_EMAC=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y