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/T1023RDB_SDCARD_defconfig b/configs/T1023RDB_SDCARD_defconfig
index 641b392..516692e 100644
--- a/configs/T1023RDB_SDCARD_defconfig
+++ b/configs/T1023RDB_SDCARD_defconfig
@@ -46,6 +46,7 @@
 CONFIG_CMD_MTDPARTS=y
 CONFIG_MTDIDS_DEFAULT="nor0=fe8000000.nor,nand0=fff800000.flash,spi0=spife110000.1"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=fe8000000.nor:1m(uboot),5m(kernel),128k(dtb),96m(fs),-(user);fff800000.flash:1m(uboot),5m(kernel),128k(dtb),96m(fs),-(user);spife110000.0:1m(uboot),5m(kernel),128k(dtb),-(user)"
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_FSL_CAAM=y
 CONFIG_FSL_ESDHC=y