systemc: Add an sc_gem5::Port destructor.

This destructor just removes the port from the list of all ports.

Change-Id: I809b529540c2946d20aeb8d64467d77dc94a7a96
Reviewed-on: https://gem5-review.googlesource.com/c/13288
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/systemc/core/port.hh

@@ -147,6 +147,8 @@ class Port
         allPorts.push_front(this);
     }
 
+    ~Port() { allPorts.remove(this); }
+
     void
     bind(::sc_core::sc_interface *interface)
     {