Convert CONFIG_ENV_OVERWRITE to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_OVERWRITE

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Rerun migration, remove some comments]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/MPC832XEMDS_HOST_66_defconfig b/configs/MPC832XEMDS_HOST_66_defconfig
index 5eca9b2..6a35a9c 100644
--- a/configs/MPC832XEMDS_HOST_66_defconfig
+++ b/configs/MPC832XEMDS_HOST_66_defconfig
@@ -149,6 +149,7 @@
 CONFIG_CMD_PCI=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_PING=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_ADDR=0xFE080000
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y