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>

vmm/src/api/openapi/cloud-hypervisor.yaml

@@ -1073,11 +1073,19 @@ components:
         - src
       type: object
       properties:
-        src:
+        id:
           type: string
+        pci_segment:
+          type: integer
+          format: int16
+        pci_device_id:
+          type: integer
+          format: uint8
         iommu:
           type: boolean
           default: false
+        src:
+          type: string
 
     BalloonConfig:
       required: