mem: Add MemChecker and MemCheckerMonitor

This patch adds the MemChecker and MemCheckerMonitor classes. While
MemChecker can be integrated anywhere in the system and is independent,
the most convenient usage is through the MemCheckerMonitor -- this
however, puts limitations on where the MemChecker is able to observe
read/write transactions.

src/mem/SConscript

@@ -79,6 +79,10 @@ if env['HAVE_DRAMSIM']:
     Source('dramsim2_wrapper.cc')
     Source('dramsim2.cc')
 
+SimObject('MemChecker.py')
+Source('mem_checker.cc')
+Source('mem_checker_monitor.cc')
+
 DebugFlag('AddrRanges')
 DebugFlag('BaseXBar')
 DebugFlag('CoherentXBar')
@@ -99,3 +103,6 @@ DebugFlag('MemoryAccess')
 DebugFlag('PacketQueue')
 
 DebugFlag("DRAMSim2")
+
+DebugFlag("MemChecker")
+DebugFlag("MemCheckerMonitor")