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/strider_cpu_dp_defconfig b/configs/strider_cpu_dp_defconfig
index 01cdf0c..4145e20 100644
--- a/configs/strider_cpu_dp_defconfig
+++ b/configs/strider_cpu_dp_defconfig
@@ -120,6 +120,7 @@
 CONFIG_CMD_PING=y
 CONFIG_CMD_EXT2=y
 CONFIG_DOS_PARTITION=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_ENV_ADDR=0xFE060000
 CONFIG_ENV_ADDR_REDUND=0xFE070000