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/pm9261_defconfig b/configs/pm9261_defconfig
index 4999285..edeaf8f 100644
--- a/configs/pm9261_defconfig
+++ b/configs/pm9261_defconfig
@@ -31,6 +31,7 @@
 CONFIG_MTDIDS_DEFAULT="nor0=physmap-flash.0,nand0=nand"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=physmap-flash.0:256k(u-boot)ro,64k(u-boot-env)ro,1408k(kernel),-(rootfs);nand:-(nand)"
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_ENV_ADDR=0x10040000
 CONFIG_DM=y