configs,ext,stdlib: Update DRAMSys integration

Recent breaking changes in the DRAMSys API require user code to be
updated. These updates have been applied to the gem5 integration.

Furthermore, as DRAMSys started to use CMake dependency management,
it is no longer sensible to maintain two separate build systems for
DRAMSys. The use of the DRAMSys integration in gem5 will therefore
from now on require that CMake is installed on the target machine.

Additionally, support for snapshots have been implemented into DRAMSys
and coupled with gem5's checkpointing API.

Change-Id: I1ab25deba2a8478ff97c477694813ac123d60379

src/mem/SConscript

@@ -124,6 +124,7 @@ if env['HAVE_DRAMSIM3']:
 if env['HAVE_DRAMSYS']:
     SimObject('DRAMSys.py', sim_objects=['DRAMSys'])
     Source('dramsys_wrapper.cc')
+    Source('dramsys.cc')
 
 SimObject('MemChecker.py', sim_objects=['MemChecker', 'MemCheckerMonitor'])
 Source('mem_checker.cc')