pci, vmm: Extend PciDevice trait to support BAR relocation

By adding a new method id() to the PciDevice trait, we allow the caller
to retrieve a unique identifier. This is used in the context of BAR
relocation to identify the device being relocated, so that we can update
the DeviceTree resources for all PCI devices (and not only
VirtioPciDevice).

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/transport/pci_device.rs

@@ -1089,6 +1089,10 @@ impl PciDevice for VirtioPciDevice {
     fn as_any(&mut self) -> &mut dyn Any {
         self
     }
+
+    fn id(&self) -> Option<String> {
+        Some(self.id.clone())
+    }
 }
 
 impl BusDevice for VirtioPciDevice {