Move the port from base memory object into the physical memory object.

Move the port from base memory object into the physical memory object.
The Memory is now a pure virtual base class for all memory type objects (DRAM, physical).
We should consider renaming MemObject to something more meaningful to represent it is for all memory heirarchy objects, perhaps MemHeirObject?

mem/physical.cc:
mem/physical.hh:
    Move the port from the base class into the actual object.

--HG--
extra : convert_revision : b7754ee7b90fd8f816f9876dce374c1d43c7e34b