Convert CONFIG_MII_INIT to Kconfig

This converts the following to Kconfig:
   CONFIG_MII_INIT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/M5235EVB_Flash32_defconfig b/configs/M5235EVB_Flash32_defconfig
index a3762bb..7552741 100644
--- a/configs/M5235EVB_Flash32_defconfig
+++ b/configs/M5235EVB_Flash32_defconfig
@@ -20,6 +20,7 @@
 CONFIG_CMD_DHCP=y
 CONFIG_BOOTP_BOOTFILESIZE=y
 CONFIG_CMD_MII=y
+CONFIG_MII_INIT=y
 CONFIG_CMD_PING=y
 CONFIG_CMD_CACHE=y
 CONFIG_ENV_IS_IN_FLASH=y