vfio/pci: Bypass IGD init in case of -ENODEV

Bypass the IGD initialization when -ENODEV returns,
that should be the case if opregion is not available for IGD
or within discrete graphics device's option ROM,
or host/lpc bridge is not found.

Then use of -ENODEV here means no special device resources found
which needs special care for VFIO, but we still allow other normal
device resource access.

Cc: Zhenyu Wang <[e-mail]>
Cc: Xiong Zhang <[e-mail]>
Cc: Hang Yuan <[e-mail]>
Cc: Stuart Summers <[e-mail]>
Signed-off-by: Fred Gao <[e-mail]>
Signed-off-by: Alex Williamson <[e-mail]>

drivers/vfio/pci/vfio_pci.c

···
 	    pdev->vendor == PCI_VENDOR_ID_INTEL &&
 	    IS_ENABLED(CONFIG_VFIO_PCI_IGD)) {
 		ret = vfio_pci_igd_init(vdev);
-		if (ret) {
+		if (ret && ret != -ENODEV) {
 			pci_warn(pdev, "Failed to setup Intel IGD regions\n");
 			goto disable_exit;
 		}