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/bk4r1_defconfig b/configs/bk4r1_defconfig
index 8fab4fc..32abe37 100644
--- a/configs/bk4r1_defconfig
+++ b/configs/bk4r1_defconfig
@@ -41,6 +41,7 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=vf610_nfc:2048k(bootloader),128k(env1),128k(env2),10240k(initrd),40960k(dtbkernel),-(system);NOR:-(nor)"
 CONFIG_CMD_UBI=y
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y