test: Skip flat-tree tests if devicetree is not used

Many tests don't actually use the devicetree at all so there is no point
in running the tests both with livetree and flat tree. Check for this and
skip the flat tree test in that case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/test/test-main.c b/test/test-main.c
index 2a3b2ba..778bf0a 100644
--- a/test/test-main.c
+++ b/test/test-main.c
@@ -476,7 +476,8 @@
 	 *   (for sandbox we handle this by copying the tree, but not for other
 	 *    boards)
 	 */
-	if (!(test->flags & UT_TESTF_LIVE_TREE) &&
+	if ((test->flags & UT_TESTF_SCAN_FDT) &&
+	    !(test->flags & UT_TESTF_LIVE_TREE) &&
 	    (CONFIG_IS_ENABLED(OFNODE_MULTI_TREE) ||
 	     !(test->flags & UT_TESTF_OTHER_FDT)) &&
 	    (!runs || ut_test_run_on_flattree(test)) &&