sandbox: add test of CONFIG_ENV_IMPORT_FDT

Check that a variable defined in /config/environment is found in the
run-time environment, and that clearing fdt_env_path from within that
node works.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
[trini: Conditionalize the test being linked in]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 570af61..bdbf714 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -106,6 +106,7 @@
 CONFIG_ENV_IS_IN_EXT4=y
 CONFIG_ENV_EXT4_INTERFACE="host"
 CONFIG_ENV_EXT4_DEVICE_AND_PART="0:0"
+CONFIG_ENV_IMPORT_FDT=y
 CONFIG_BOOTP_SEND_HOSTNAME=y
 CONFIG_NETCONSOLE=y
 CONFIG_IP_DEFRAG=y