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/mx6cuboxi_defconfig b/configs/mx6cuboxi_defconfig
index b59db2e..6e73a97 100644
--- a/configs/mx6cuboxi_defconfig
+++ b/configs/mx6cuboxi_defconfig
@@ -33,6 +33,7 @@
 CONFIG_DWC_AHSATA=y
 CONFIG_FSL_ESDHC=y
 CONFIG_PHYLIB=y
+CONFIG_MII=y
 CONFIG_DM_THERMAL=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y