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/goflexhome_defconfig b/configs/goflexhome_defconfig
index 87a28f6..8af4149 100644
--- a/configs/goflexhome_defconfig
+++ b/configs/goflexhome_defconfig
@@ -33,6 +33,7 @@
 CONFIG_CMD_UBI=y
 CONFIG_ISO_PARTITION=y
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_DM=y
 CONFIG_MVSATA_IDE=y