pci: Save deferred BAR reprogramming state

OVMF can reprogram PCI BARs while memory space decoding is disabled.
Cloud Hypervisor defers the corresponding BAR move in
`pending_bar_reprogram` until the PCI command register enables Memory
Space again.

That deferred state was not part of `PciConfigurationState`. A
snapshot taken in that window restored the new BAR values in PCI
config space, but lost the pending BAR relocation needed to update the
VMM-side BAR mapping.

The restore logs show guest MMIO accesses to the reprogrammed BAR
addresses `0xc0000000`, `0x100000000`, and `0x100080000` hitting
unregistered addresses. The firmware serial output shows OVMF
assigning those same BAR addresses during PCI resource allocation,
then reaching BDS, finding the mass-storage device, and failing to
boot from it.

Serialize and restore `pending_bar_reprogram` so deferred BAR moves
survive snapshot and restore.

Co-authored-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
Co-authored-by: Julian Schindel <julian.schindel@cyberus-technology.de>
On-behalf-of: SAP leander.kohler@sap.com
Signed-off-by: Leander Kohler <leander.kohler@cyberus-technology.de>

pci/src/device.rs

@@ -8,6 +8,7 @@ use std::any::Any;
 use std::sync::{Arc, Barrier, Mutex};
 use std::{io, result};
 
+use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use vm_allocator::{AddressAllocator, SystemAllocator};
 use vm_device::Resource;
@@ -35,7 +36,7 @@ pub enum Error {
 }
 pub type Result<T> = std::result::Result<T, Error>;
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
 pub struct BarReprogrammingParams {
     pub old_base: u64,
     pub new_base: u64,