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/ti816x_evm_defconfig b/configs/ti816x_evm_defconfig
index b840f56..626bea1 100644
--- a/configs/ti816x_evm_defconfig
+++ b/configs/ti816x_evm_defconfig
@@ -43,6 +43,7 @@
 # CONFIG_ISO_PARTITION is not set
 # CONFIG_EFI_PARTITION is not set
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_NAND=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y