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/kmtegr1_defconfig b/configs/kmtegr1_defconfig
index dc09d23..58674c6 100644
--- a/configs/kmtegr1_defconfig
+++ b/configs/kmtegr1_defconfig
@@ -146,6 +146,7 @@
 CONFIG_CMD_DIAG=y
 CONFIG_CMD_UBI=y
 # CONFIG_CMD_UBIFS is not set
+CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_ENV_ADDR=0xF0100000
 CONFIG_ENV_ADDR_REDUND=0xF0120000