[sw/dif_gpio] Add GPIO smoke test

Signed-off-by: Alphan Ulusoy <alphan@google.com>
diff --git a/test/systemtest/config.py b/test/systemtest/config.py
index c12d38f..a3de7ac 100644
--- a/test/systemtest/config.py
+++ b/test/systemtest/config.py
@@ -67,4 +67,9 @@
         "name": "usbdev_test",
         "targets": ["sim_verilator"],
     },
+    # Cannot run on sim_verilator due to the differences in the top level.
+    {
+        "name": "dif_gpio_smoketest",
+        "targets": ["fpga_nexysvideo"],
+    },
 ]