configs: sandbox: activate env in ext4 support

Activate ENV in EXT4 support in sandbox.

The sandbox behavior don't change; the default environment with
the nowhere backend (CONFIG_ENV_IS_NOWHERE)is still used:
the weak function env_get_location() return ENVL_NOWHERE for priority 0.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/configs/sandbox64_defconfig b/configs/sandbox64_defconfig
index e8a1d57..9a16621 100644
--- a/configs/sandbox64_defconfig
+++ b/configs/sandbox64_defconfig
@@ -83,6 +83,10 @@
 CONFIG_OF_LIVE=y
 CONFIG_OF_HOSTFILE=y
 CONFIG_BOOTP_SEND_HOSTNAME=y
+CONFIG_ENV_IS_NOWHERE=y
+CONFIG_ENV_IS_IN_EXT4=y
+CONFIG_ENV_EXT4_INTERFACE="host"
+CONFIG_ENV_EXT4_DEVICE_AND_PART="0:0"
 CONFIG_NETCONSOLE=y
 CONFIG_IP_DEFRAG=y
 CONFIG_REGMAP=y