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/ls1021atwr_nor_SECURE_BOOT_defconfig b/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
index 49c24ae..0c0ce05 100644
--- a/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
+++ b/configs/ls1021atwr_nor_SECURE_BOOT_defconfig
@@ -33,6 +33,7 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_BMP=y
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_DM=y
 CONFIG_SATA_CEVA=y
 CONFIG_DM_I2C=y