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/am57xx_evm_defconfig b/configs/am57xx_evm_defconfig
index 229b7e5..d0f0855 100644
--- a/configs/am57xx_evm_defconfig
+++ b/configs/am57xx_evm_defconfig
@@ -59,6 +59,7 @@
 CONFIG_PHY_MICREL_KSZ90X1=y
 CONFIG_DM_ETH=y
 CONFIG_DRIVER_TI_CPSW=y
+CONFIG_MII=y
 CONFIG_DM_PMIC=y
 CONFIG_PMIC_PALMAS=y
 CONFIG_DM_REGULATOR=y