config: Support full-system with SST's memory system

This patch adds an example configuration in ext/sst/tests/ that allows
an SST/gem5 instance to simulate a 4-core AArch64 system with SST's
memHierarchy components providing all the caches and memories.

configs/common/Options.py

@@ -104,6 +104,8 @@ def addCommonOptions(parser):
     parser.add_option("--memchecker", action="store_true")
 
     # Cache Options
+    parser.add_option("--external-memory-system", type="string",
+                      help="use external ports of this port_type for caches")
     parser.add_option("--caches", action="store_true")
     parser.add_option("--l2cache", action="store_true")
     parser.add_option("--fastmem", action="store_true")