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/am43xx_hs_evm_defconfig b/configs/am43xx_hs_evm_defconfig
index e7ac746..1b8eff4 100644
--- a/configs/am43xx_hs_evm_defconfig
+++ b/configs/am43xx_hs_evm_defconfig
@@ -40,6 +40,7 @@
 CONFIG_MTDPARTS_DEFAULT="mtdparts=nand.0:256k(NAND.SPL),256k(NAND.SPL.backup1),256k(NAND.SPL.backup2),256k(NAND.SPL.backup3),512k(NAND.u-boot-spl-os),1m(NAND.u-boot),256k(NAND.u-boot-env),256k(NAND.u-boot-env.backup1),7m(NAND.kernel),-(NAND.file-system)"
 CONFIG_OF_CONTROL=y
 CONFIG_OF_LIST="am437x-gp-evm am437x-sk-evm am43x-epos-evm am437x-idk-evm"
+CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_DM=y