main, vmm: add explicit PCI BDF support for Rng device

This was missing in [0] but is required for proper explicit PCI BDF
management, e.g., when a VM is created via libvirt and each device has
an explicit BDF.

[0] https://github.com/cloud-hypervisor/cloud-hypervisor/pull/7965

On-behalf-of: SAP philipp.schuster@sap.com
Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>

fuzz/fuzz_targets/http_api.rs

@@ -165,7 +165,7 @@ impl RequestHandler for StubApiRequestHandler {
                 net: None,
                 rng: RngConfig {
                     src: PathBuf::from("/dev/urandom"),
-                    iommu: false,
+                    pci_common: PciDeviceCommonConfig::default(),
                 },
                 balloon: None,
                 fs: None,