Update deprecated option for pci passthrough

This commit moves the deprecated pci_passthrough_whitelist option from the
[DEFAULT] section of nova.conf to the [pci] section as passthrough_whitelist.

Change-Id: I13b734e60d5155c3f695a19cda180b4a2e4c027d
Closes-Bug: #1795052

templates/nova.conf.j2

@@ -59,11 +59,6 @@ libvirt_vif_type = ethernet
 vif_plugging_timeout = 10
 vif_plugging_is_fatal = False
 
-{% if nova_pci_passthrough_whitelist  %}
-# PCI Passthrough
-pci_passthrough_whitelist = "{{ nova_pci_passthrough_whitelist }}"
-{% endif %}
-
 # Hypervisor
 default_ephemeral_format = ext4
 
@@ -350,3 +345,9 @@ compute=auto
 [devices]
 enabled_vgpu_types = {{ enabled_vgpu_types | join(',') }}
 {% endif %}
+
+{% if nova_pci_passthrough_whitelist  %}
+[pci]
+# White list of PCI devices available to VMs.
+passthrough_whitelist = "{{ nova_pci_passthrough_whitelist }}"
+{% endif %}