tools/testing/cxl: Add a physical_node link

Emulate what ACPI does to link a host bridge platform firmware device to
device node on the PCI bus. In this case it's just self referencing
link, but it otherwise lets the tooling test out its lookup code.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

tools/testing/cxl/test/cxl.c

···
 			platform_device_put(pdev);
 			goto err_bridge;
 		}
+
 		cxl_host_bridge[i] = pdev;
+		rc = sysfs_create_link(&pdev->dev.kobj, &pdev->dev.kobj,
+				       "physical_node");
+		if (rc)
+			goto err_bridge;
 	}
 
 	for (i = 0; i < ARRAY_SIZE(cxl_root_port); i++) {
···
 	for (i = ARRAY_SIZE(cxl_root_port) - 1; i >= 0; i--)
 		platform_device_unregister(cxl_root_port[i]);
 err_bridge:
-	for (i = ARRAY_SIZE(cxl_host_bridge) - 1; i >= 0; i--)
+	for (i = ARRAY_SIZE(cxl_host_bridge) - 1; i >= 0; i--) {
+		struct platform_device *pdev = cxl_host_bridge[i];
+
+		if (!pdev)
+			continue;
+		sysfs_remove_link(&pdev->dev.kobj, "physical_node");
 		platform_device_unregister(cxl_host_bridge[i]);
+	}
 err_populate:
 	depopulate_all_mock_resources();
 err_gen_pool_add:
···
 		platform_device_unregister(cxl_switch_uport[i]);
 	for (i = ARRAY_SIZE(cxl_root_port) - 1; i >= 0; i--)
 		platform_device_unregister(cxl_root_port[i]);
-	for (i = ARRAY_SIZE(cxl_host_bridge) - 1; i >= 0; i--)
+	for (i = ARRAY_SIZE(cxl_host_bridge) - 1; i >= 0; i--) {
+		struct platform_device *pdev = cxl_host_bridge[i];
+
+		if (!pdev)
+			continue;
+		sysfs_remove_link(&pdev->dev.kobj, "physical_node");
 		platform_device_unregister(cxl_host_bridge[i]);
+	}
 	depopulate_all_mock_resources();
 	gen_pool_destroy(cxl_mock_pool);
 	unregister_cxl_mock_ops(&cxl_mock_ops);