misc: Add secondary dot output for DVFS domains

This patch adds a secondary dot output file which shows the DVFS domains. This
has been done separately for now to avoid cluttering the already existing
diagram. Due to the way that the clock domains are assigned to components in
gem5, this output must be generated after the C++ objects have been
instantiated. This further motivates the need to generate this file separately
to the current dot output, and not to replace it entirely.

src/python/m5/main.py

@@ -91,6 +91,9 @@ def parse_options():
         help="Create JSON output of the configuration [Default: %default]")
     option("--dot-config", metavar="FILE", default="config.dot",
         help="Create DOT & pdf outputs of the configuration [Default: %default]")
+    option("--dot-dvfs-config", metavar="FILE", default="config_dvfs.dot",
+        help="Create DOT & pdf outputs of the DVFS configuration" + \
+             " [Default: %default]")
 
     # Debugging options
     group("Debugging Options")