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/test/env/Makefile b/test/env/Makefile
index 5c8eae3..9a98fd4 100644
--- a/test/env/Makefile
+++ b/test/env/Makefile
@@ -5,3 +5,4 @@
 obj-y += cmd_ut_env.o
 obj-y += attr.o
 obj-y += hashtable.o
+obj-$(CONFIG_ENV_IMPORT_FDT) += fdt.o