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/M5282EVB_defconfig b/configs/M5282EVB_defconfig
index 84363fb..69db87c 100644
--- a/configs/M5282EVB_defconfig
+++ b/configs/M5282EVB_defconfig
@@ -17,6 +17,7 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_BOOTP_BOOTFILESIZE=y
 CONFIG_CMD_MII=y
+CONFIG_MII_INIT=y
 CONFIG_CMD_PING=y
 CONFIG_CMD_CACHE=y
 CONFIG_ENV_ADDR=0xFFE04000