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/colibri_vf_defconfig b/configs/colibri_vf_defconfig
index f615aa0..64bd00d 100644
--- a/configs/colibri_vf_defconfig
+++ b/configs/colibri_vf_defconfig
@@ -54,6 +54,7 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=vf610_nfc:128k(vf-bcb)ro,1408k(u-boot)ro,512k(u-boot-env),-(ubi)"
 CONFIG_CMD_UBI=y
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y