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/platinum_titanium_defconfig b/configs/platinum_titanium_defconfig
index 659af53..b37eb60 100644
--- a/configs/platinum_titanium_defconfig
+++ b/configs/platinum_titanium_defconfig
@@ -50,6 +50,7 @@
 CONFIG_MTDIDS_DEFAULT="nand0=gpmi-nand"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=gpmi-nand:14M(spl),2M(uboot),512k(env1),512k(env2),-(ubi)"
 CONFIG_CMD_UBI=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y