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/pico-imx7d_defconfig b/configs/pico-imx7d_defconfig
index 98b5c01..d6cfc20 100644
--- a/configs/pico-imx7d_defconfig
+++ b/configs/pico-imx7d_defconfig
@@ -48,6 +48,7 @@
 CONFIG_FASTBOOT_CMD_OEM_FORMAT=y
 CONFIG_FSL_ESDHC=y
 CONFIG_PHYLIB=y
+CONFIG_MII=y
 CONFIG_USB=y
 CONFIG_USB_EHCI_HCD=y
 CONFIG_MXC_USB_OTG_HACTIVE=y