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/uDPU_defconfig b/configs/uDPU_defconfig
index 55123db..dfab2b3 100644
--- a/configs/uDPU_defconfig
+++ b/configs/uDPU_defconfig
@@ -46,6 +46,7 @@
 CONFIG_MTDIDS_DEFAULT="nor0=spi0"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=spi0:4m(uboot),-(rootfs)"
 CONFIG_MAC_PARTITION=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NET_RANDOM_ETHADDR=y