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/am65x_evm_r5_defconfig b/configs/am65x_evm_r5_defconfig
index f7e4c80..9e1da64 100644
--- a/configs/am65x_evm_r5_defconfig
+++ b/configs/am65x_evm_r5_defconfig
@@ -59,6 +59,7 @@
 CONFIG_SPL_OF_CONTROL=y
 CONFIG_SPL_MULTI_DTB_FIT=y
 CONFIG_SPL_MULTI_DTB_FIT_NO_COMPRESSION=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_FAT=y
 CONFIG_ENV_FAT_DEVICE_AND_PART="1:1"
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y