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/dra7xx_hs_evm_defconfig b/configs/dra7xx_hs_evm_defconfig
index f7b7c59..c71f2dd 100644
--- a/configs/dra7xx_hs_evm_defconfig
+++ b/configs/dra7xx_hs_evm_defconfig
@@ -52,6 +52,7 @@
 CONFIG_SPL_MULTI_DTB_FIT=y
 CONFIG_SPL_MULTI_DTB_FIT_UNCOMPRESS_SZ=0xA000
 CONFIG_OF_SPL_REMOVE_PROPS="clocks clock-names interrupt-parent"
+CONFIG_ENV_OVERWRITE=y
 # CONFIG_ENV_IS_IN_FAT is not set
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y