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/galileo_defconfig b/configs/galileo_defconfig
index 5990cf6..5f89a38 100644
--- a/configs/galileo_defconfig
+++ b/configs/galileo_defconfig
@@ -37,6 +37,7 @@
 CONFIG_MAC_PARTITION=y
 CONFIG_ISO_PARTITION=y
 CONFIG_EFI_PARTITION=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_REGMAP=y