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/gplugd_defconfig b/configs/gplugd_defconfig
index f387d3d..75ce289 100644
--- a/configs/gplugd_defconfig
+++ b/configs/gplugd_defconfig
@@ -16,6 +16,7 @@
 CONFIG_CMD_FAT=y
 CONFIG_ISO_PARTITION=y
 # CONFIG_MMC is not set
+CONFIG_MII=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y