The MemoryObject tha owns a port should delete it if it so chooses when deletePortRef...

The MemoryObject tha owns a port should delete it if it so chooses when deletePortRefs() is called on it with that port as a parameter.
In this way a MemoryObject can keep a functional port around and give it to anyone who wants to do functional accesses rather
than creating a new one each time.

src/mem/bus.cc:
src/mem/bus.hh:
src/mem/cache/cache_impl.hh:
    only keep around one func port we give to anyone who wants it. Otherwise we can run out of port ids reasonably quickly if
    a lot of functional accesses are happening (e.g. remote debugging, dprintk, etc)

--HG--
extra : convert_revision : 6a9e3e96f51cedaab6de1b36cf317203899a3716