vfio/pci: match IGD devices in display controller class

vfio/pci: match IGD devices in display controller class

IGD device can either expose as a VGA controller or display controller
depending on whether it is configured as the primary display device in
BIOS. In both cases, the OpRegion may be present. A new helper function
vfio_pci_is_intel_display() is introduced to check if the device might
be an IGD device.

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Link: https://lore.kernel.org/r/20250123163416.7653-1-tomitamoeko@gmail.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>