configs: ls1012a/ls1046a: Add CONFIG_ENV_OVERWRITE in defconfig

CONFIG_ENV_OVERWRITE disables write protection on various environment
variables like "ethaddr" and "serial".

Enable this config in LS1046A and LS1012A defconfigs. This resolves an
error while setting multiple values of "ethaddr" variable.

Before the change:
=> setenv ethaddr 00:E0:0C:00:06:0
=> setenv ethaddr 00:E0:0C:00:06:1
Error: Can't overwrite "ethaddr"
Error inserting "ethaddr" variable, errno=1

After the change:
=> setenv ethaddr 00:E0:0C:00:06:0
=> setenv ethaddr 00:E0:0C:00:06:1

Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/configs/ls1012ardb_qspi_SECURE_BOOT_defconfig b/configs/ls1012ardb_qspi_SECURE_BOOT_defconfig
index 1f403d5..552364a 100644
--- a/configs/ls1012ardb_qspi_SECURE_BOOT_defconfig
+++ b/configs/ls1012ardb_qspi_SECURE_BOOT_defconfig
@@ -35,6 +35,7 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_CACHE=y
 CONFIG_OF_CONTROL=y
+CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_DM=y