mem: Make the BaseXBar public to not confuse Python wrappers

The Python wrappers generally assume that destructors are public. Make
the BaseXBar destructor public to avoid confusing the Python wrapper.

Change-Id: If958802409c0be74e875dd6e279742abfdb3ede1
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>

src/mem/xbar.hh

@@ -439,8 +439,6 @@ class BaseXBar : public MemObject
 
     BaseXBar(const BaseXBarParams *p);
 
-    virtual ~BaseXBar();
-
     /**
      * Stats for transaction distribution and data passing through the
      * crossbar. The transaction distribution is globally counting
@@ -456,6 +454,8 @@ class BaseXBar : public MemObject
 
   public:
 
+    virtual ~BaseXBar();
+
     virtual void init();
 
     /** A function used to return the port associated with this object. */