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/vf610twr_defconfig b/configs/vf610twr_defconfig
index c179e28..a9e6ca9 100644
--- a/configs/vf610twr_defconfig
+++ b/configs/vf610twr_defconfig
@@ -32,6 +32,7 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=fsl_nfc:128k(vf-bcb)ro,1408k(u-boot)ro,512k(u-boot-env),4m(kernel),512k(fdt),-(rootfs)"
 CONFIG_CMD_UBI=y
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_DM=y