py: tests: Fix configspec marking for nand tests

Fix marking for nand tests. Create multiple markers.

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

test/py/tests/test_nand.py

@@ -18,7 +18,9 @@ TODO:
 - Handle multiple controller cases, as of now it assumes one.
 
 """
-pytestmark = pytest.mark.buildconfigspec('cmd_bdi cmd_nand cmd_memory')
+pytestmark = [pytest.mark.buildconfigspec("cmd_bdi"),
+	      pytest.mark.buildconfigspec("cmd_nand"),
+	      pytest.mark.buildconfigspec("cmd_memory")]
 
 nand_detected = False
 page_size = 0