gem5: pydot to generate config.ini graphs

configure

@@ -45,6 +45,8 @@ protobuf-compiler \
 python-dev \
 scons \
 "
+  # Generate graphs of config.ini under m5out.
+  pip install --user pydot
 fi
 command -v apt-get >/dev/null 2>&1 || {
   cat <<EOF