stdlib: Add _pre_instantiate funcs for caches and memory

Note: At present this is not used but these functions can be filled
or overriden in subclasses as required.

src/python/gem5/components/boards/abstract_board.py

@@ -420,8 +420,10 @@ class AbstractBoard:
         )
 
         # 3. Call any of the components' `_pre_instantiate` functions.
-        # Right now, only the processor requires this.
         self.get_processor()._pre_instantiate(root)
+        self.get_memory()._pre_instantiate(root)
+        if self.get_cache_hierarchy():
+            self.get_cache_hierarchy()._pre_instantiate(root)
 
         # 4. Return the root object.
         return root

src/python/gem5/components/cachehierarchies/abstract_cache_hierarchy.py

@@ -42,7 +42,10 @@ from abc import (
 )
 from typing import Callable
 
-from m5.objects import SubSystem
+from m5.objects import (
+    Root,
+    SubSystem,
+)
 from m5.util.fdthelper import *
 
 from ..boards.abstract_board import AbstractBoard
@@ -139,6 +142,18 @@ class AbstractCacheHierarchy(SubSystem):
         """
         raise NotImplementedError
 
+    def _pre_instantiate(self, root: Root) -> None:
+        """Called in the `AbstractBoard`'s `_pre_instantiate` method. This is
+        called after `connect_things`, after the creation of the root object
+        (which is passed in as an argument), but before `m5.instantiate`).
+
+        Subclasses should override this method to set up any connections.
+
+        At present there is no general task that must be specified here and is
+        default or applicable to all cache hierarchies.
+        """
+        pass
+
     def _post_instantiate(self):
         """Called to set up anything needed after ``m5.instantiate``."""
         pass

src/python/gem5/components/memory/abstract_memory_system.py

@@ -38,6 +38,7 @@ from m5.objects import (
     AddrRange,
     MemCtrl,
     Port,
+    Root,
     SubSystem,
 )
 
@@ -50,6 +51,18 @@ class AbstractMemorySystem(SubSystem):
     def __init__(self) -> None:
         super().__init__()
 
+    def _pre_instantiate(self, root: Root) -> None:
+        """Called in the `AbstractBoard`'s `_pre_instantiate` method. This is
+        called after `connect_things`, after the creation of the root object
+        (which is passed in as an argument), but before `m5.instantiate`).
+
+        Subclasses should override this method to set up any connections.
+
+        At present there is no general task that must be specified here and is
+        default or applicable to all memory systems.
+        """
+        pass
+
     @abstractmethod
     def incorporate_memory(self, board: AbstractBoard) -> None:
         """This function completes all of the necessary steps to add this