config: Break out base options for usage with NULL ISA

This patch breaks out the most basic configuration options into a set
of base options, to allow them to be used also by scripts that do not
involve any ISA, and thus no actual CPUs or devices.

The patch also fixes a few modules so that they can be imported in a
NULL build, and avoid dragging in FSConfig every time Options is
imported.

configs/example/ruby_direct_test.py

@@ -45,7 +45,7 @@ config_root = os.path.dirname(config_path)
 m5_root = os.path.dirname(config_root)
 
 parser = optparse.OptionParser()
-Options.addCommonOptions(parser)
+Options.addNoISAOptions(parser)
 
 parser.add_option("--requests", metavar="N", default=100,
                   help="Stop after N requests")