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/mx35pdk_defconfig b/configs/mx35pdk_defconfig
index 0af0afc..34e5559 100644
--- a/configs/mx35pdk_defconfig
+++ b/configs/mx35pdk_defconfig
@@ -26,6 +26,7 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=mxc_nand:1m(boot),5m(linux),96m(root),8m(cfg),1938m(user);physmap-flash.0:512k(b),4m(k),30m(u),28m(r)"
 CONFIG_EFI_PARTITION=y
 # CONFIG_PARTITION_UUIDS is not set
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_ENV_ADDR=0xA0080000