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/imx6q_logic_defconfig b/configs/imx6q_logic_defconfig
index 4300c30..6bc5a73 100644
--- a/configs/imx6q_logic_defconfig
+++ b/configs/imx6q_logic_defconfig
@@ -60,6 +60,7 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=gpmi-nand:2m(spl),2m(uboot),1m(env),16m(kernel),1m(dtb),-(fs)"
 CONFIG_CMD_UBI=y
 CONFIG_SPL_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_FAT=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_ENV_FAT_DEVICE_AND_PART="0:1"