PCI/PM: Print config space of devices before suspend

When resuming from hibernation (S4, also known as "suspend to disk") on a
VM, we have seen invalid config space, e.g.,

  serial 0000:00:16.3: restoring config space at offset 0x14 (was 0x9104e000, writing 0xffffffff)

To help debug problems like this, log the config space being saved before
suspend, similar to the log in pci_restore_config_dword() when resuming.

Link: https://lore.kernel.org/r/20200113060724.19571-1-yu.c.chen@intel.com
[bhelgaas: commit log]
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Len Brown <lenb@kernel.org>

drivers/pci/pci.c

@@ -1372,8 +1372,11 @@ int pci_save_state(struct pci_dev *dev)
 {
 	int i;
 	/* XXX: 100% dword access ok here? */
-	for (i = 0; i < 16; i++)
+	for (i = 0; i < 16; i++) {
 		pci_read_config_dword(dev, i * 4, &dev->saved_config_space[i]);
+		pci_dbg(dev, "saving config space at offset %#x (reading %#x)\n",
+			i * 4, dev->saved_config_space[i]);
+	}
 	dev->state_saved = true;
 
 	i = pci_save_pcie_state(dev);