Convert CONFIG_OVERWRITE_ETHADDR_ONCE to Kconfig

This converts the following to Kconfig:
   CONFIG_OVERWRITE_ETHADDR_ONCE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/M5253DEMO_defconfig b/configs/M5253DEMO_defconfig
index 4de6290..ea07997 100644
--- a/configs/M5253DEMO_defconfig
+++ b/configs/M5253DEMO_defconfig
@@ -25,6 +25,7 @@
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y
 CONFIG_MAC_PARTITION=y
+CONFIG_OVERWRITE_ETHADDR_ONCE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_USE_HOSTNAME=y
 CONFIG_HOSTNAME="M5253DEMO"