tools/testing/cxl: Add bridge mocking support

In preparation for cxl_acpi walking pci_root->bus->bridge, add that
association to the mock pci_root instances.

Note that the missing 3rd entry in mock_pci_root[] was not noticed until
now given that the test version of to_cxl_host_bridge()
(tools/testing/cxl/mock_acpi.c), obviated the need for that entry.
However, "cxl/acpi: Improve debug messages in cxl_acpi_probe()" [1]
needs pci_root->bus->bridge to be populated.

Link: https://lore.kernel.org/r/20221018132341.76259-6-rrichter@amd.com [1]
Cc: Robert Richter <rrichter@amd.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

tools/testing/cxl/test/cxl.c

@@ -439,14 +439,18 @@ mock_acpi_evaluate_integer(acpi_handle handle, acpi_string pathname,
 	return AE_OK;
 }
 
-static struct pci_bus mock_pci_bus[NR_CXL_HOST_BRIDGES];
-static struct acpi_pci_root mock_pci_root[NR_CXL_HOST_BRIDGES] = {
+static struct pci_bus mock_pci_bus[NR_CXL_HOST_BRIDGES + NR_CXL_SINGLE_HOST];
+static struct acpi_pci_root mock_pci_root[ARRAY_SIZE(mock_pci_bus)] = {
 	[0] = {
 		.bus = &mock_pci_bus[0],
 	},
 	[1] = {
 		.bus = &mock_pci_bus[1],
 	},
+	[2] = {
+		.bus = &mock_pci_bus[2],
+	},
+
 };
 
 static bool is_mock_bus(struct pci_bus *bus)
@@ -744,6 +748,7 @@ static __init int cxl_single_init(void)
 		}
 
 		cxl_hb_single[i] = pdev;
+		mock_pci_bus[i + NR_CXL_HOST_BRIDGES].bridge = &pdev->dev;
 		rc = sysfs_create_link(&pdev->dev.kobj, &pdev->dev.kobj,
 				       "physical_node");
 		if (rc)
@@ -910,6 +915,7 @@ static __init int cxl_test_init(void)
 		}
 
 		cxl_host_bridge[i] = pdev;
+		mock_pci_bus[i].bridge = &pdev->dev;
 		rc = sysfs_create_link(&pdev->dev.kobj, &pdev->dev.kobj,
 				       "physical_node");
 		if (rc)