test/py: Add simple dm commands run without checking

Just to make sure that dm commands can operate.
This was problem on Microblaze in past.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

test/py/tests/test_dm.py

@@ -0,0 +1,17 @@
+# Copyright (c) 2016, Xilinx Inc. Michal Simek
+#
+# SPDX-License-Identifier: GPL-2.0
+
+import pytest
+
+@pytest.mark.buildconfigspec("cmd_dm")
+def test_dm_tree(u_boot_console):
+    response = u_boot_console.run_command("dm tree")
+
+@pytest.mark.buildconfigspec("cmd_dm")
+def test_dm_uclass(u_boot_console):
+    response = u_boot_console.run_command("dm uclass")
+
+@pytest.mark.buildconfigspec("cmd_dm")
+def test_dm_devres(u_boot_console):
+    response = u_boot_console.run_command("dm devres")