pci: Make Python wrapper cast to the right type

The PCI base class is PciDev and not PciDevice, which is used by the
Python world. Make sure this is reflected in the wrapper code.

src/dev/Pci.py

@@ -41,6 +41,7 @@ class PciConfigAll(PioDevice):
 
 class PciDevice(DmaDevice):
     type = 'PciDevice'
+    cxx_class = 'PciDev'
     abstract = True
     platform = Param.Platform(Parent.any, "Platform this device is part of.")
     config = SlavePort("PCI configuration space port")