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/axs103_defconfig b/configs/axs103_defconfig
index e524e6a..aefabcd 100644
--- a/configs/axs103_defconfig
+++ b/configs/axs103_defconfig
@@ -44,6 +44,7 @@
 CONFIG_DM_ETH=y
 CONFIG_PHY_GIGE=y
 CONFIG_ETH_DESIGNWARE=y
+CONFIG_MII=y
 CONFIG_DM_SERIAL=y
 CONFIG_DEBUG_UART_SHIFT=2
 CONFIG_DEBUG_UART_ANNOUNCE=y