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/nsa310s_defconfig b/configs/nsa310s_defconfig
index 32c1511..4a9ec13 100644
--- a/configs/nsa310s_defconfig
+++ b/configs/nsa310s_defconfig
@@ -25,8 +25,8 @@
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_MVSATA_IDE=y
 # CONFIG_MMC is not set
-CONFIG_NETDEVICES=y
 CONFIG_MVGBE=y
+CONFIG_MII=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y