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/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index d58ab7b..fb08ba5 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -65,6 +65,7 @@
 CONFIG_SPI_FLASH_SST=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_PHYLIB=y
+CONFIG_MII=y
 CONFIG_DM_PMIC=y
 CONFIG_DM_REGULATOR=y
 CONFIG_SPI=y