msix: Add SystemAllocator to MsixConfig

The point here is to let MsixConfig take care of the GSI allocation,
which means the SystemAllocator must be passed from the vmm crate all
the way down to the pci crate.

Once this is done, the GSI allocation and irq_fd creation is performed
by MsixConfig directly.

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

vmm/src/device_manager.rs

@@ -1465,12 +1465,17 @@ impl DeviceManager {
                 None
             };
 
-        let mut virtio_pci_device =
-            VirtioPciDevice::new(memory.clone(), virtio_device, msix_num, iommu_mapping_cb)
-                .map_err(DeviceManagerError::VirtioDevice)?;
-
         let mut allocator = address_manager.allocator.lock().unwrap();
 
+        let mut virtio_pci_device = VirtioPciDevice::new(
+            memory.clone(),
+            virtio_device,
+            msix_num,
+            iommu_mapping_cb,
+            &mut allocator,
+        )
+        .map_err(DeviceManagerError::VirtioDevice)?;
+
         let bars = virtio_pci_device
             .allocate_bars(&mut allocator)
             .map_err(DeviceManagerError::AllocateBars)?;