Move provider_tree RP creation to PciResourceProvider

It is a simple refactor to move the actual RP creation under the scope
of PciResourceProvider.update_provider_tree to remove the assumption the
RPs are always pre-created by the caller in the provider_tree.

blueprint: pci-device-tracking-in-placement
Change-Id: I375a1fb013a8e877c159b907484ba16871935879

Author: gibizer

nova/compute/pci_placement_translator.py

@@ -178,7 +178,9 @@ def remove_parent(self, dev: pci_device.PciDevice) -> None:
         pass
 
     def update_provider_tree(
-        self, provider_tree: provider_tree.ProviderTree
+        self,
+        provider_tree: provider_tree.ProviderTree,
+        parent_rp_name: str,
     ) -> None:
 
         if not self.parent_dev and not self.children_devs:
@@ -191,6 +193,9 @@ def update_provider_tree(
 
             return
 
+        if not provider_tree.exists(self.name):
+            provider_tree.new_child(self.name, parent_rp_name)
+
         provider_tree.update_inventory(
             self.name,
             # NOTE(gibi): The rest of the inventory fields (reserved,
@@ -341,10 +346,7 @@ def update_provider_tree(
         self, provider_tree: provider_tree.ProviderTree
     ) -> None:
         for rp_name, rp in self.rps.items():
-            if not provider_tree.exists(rp_name):
-                provider_tree.new_child(rp_name, self.root_rp_name)
-
-            rp.update_provider_tree(provider_tree)
+            rp.update_provider_tree(provider_tree, self.root_rp_name)
 
 
 def ensure_no_dev_spec_with_devname(dev_specs: ty.List[devspec.PciDeviceSpec]):