docs: Update the relevant documentation

Some of the documentation references PCI segment ID. For those documents
add a mention of the new PCI device ID.

Signed-off-by: Rob Bradford <rbradford@meta.com>

docs/device_model.md

@@ -90,8 +90,9 @@ feature is enabled by default.
 
 For all virtio devices listed below, only `virtio-pci` transport layer is
 supported. Cloud Hypervisor supports multiple PCI segments, and users can
-append `,pci_segment=<PCI_segment_number>` to the device flag in the Cloud
-Hypervisor command line to assign devices to a specific PCI segment.
+append `,pci_segment=<PCI_segment_number>` or `,pci_device_id=<PCI_device_ID>` to
+the device flag in the Cloud Hypervisor command line to assign devices to a specific
+PCI segment or into a specific device slot.
 
 ### virtio-block
 

docs/vdpa.md

@@ -32,11 +32,12 @@ struct VdpaConfig {
     iommu: bool,
     id: Option<String>,
     pci_segment: u16,
+    pci_device_id: Option<u8>
 }
 ```
 
 ```
---vdpa <vdpa>	vDPA device "path=<device_path>,num_queues=<number_of_queues>,iommu=on|off,id=<device_id>,pci_segment=<segment_id>"
+--vdpa <vdpa>	vDPA device "path=<device_path>,num_queues=<number_of_queues>,iommu=on|off,id=<device_id>,pci_segment=<segment_id>,pci_device_id=<pci_slot>"
 ```
 
 ### `path`
@@ -96,6 +97,21 @@ _Example_
 --vdpa path=/dev/vhost-vdpa-0,pci_segment=1
 ```
 
+### `pci_device_id`
+
+PCI device ID to assign to the vDPA device on its PCI bus.
+
+This parameter is optional. If not specified, a device ID is automatically
+allocated.
+
+Value is an unsigned integer in the range 1-31.
+
+_Example_
+
+```
+--vdpa path=/dev/vhost-vdpa-0,pci_device_id=5
+```
+
 ## Example with vDPA block simulator
 
 The vDPA framework provides a simulator with both `virtio-block` and