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/am43xx_evm_defconfig b/configs/am43xx_evm_defconfig
index 06e6c0d..1e80bf9 100644
--- a/configs/am43xx_evm_defconfig
+++ b/configs/am43xx_evm_defconfig
@@ -38,6 +38,7 @@
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_DRIVER_TI_CPSW=y
 CONFIG_PHY_GIGE=y
+CONFIG_MII=y
 CONFIG_DM_SERIAL=y
 CONFIG_SYS_NS16550=y
 CONFIG_SPI=y