function-graph: add option to calculate graph time or not

graph time is the time that a function is executing another function.
Thus if function A calls B, if graph-time is set, then the time for
A includes B. This is the default behavior. But if graph-time is off,
then the time spent executing B is subtracted from A.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 015a3d2..9e0a8d2 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -365,6 +365,7 @@
 	unsigned long ret;
 	unsigned long func;
 	unsigned long long calltime;
+	unsigned long long subtime;
 };
 
 /*
@@ -376,8 +377,6 @@
 
 extern int
 ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth);
-extern void
-ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret);
 
 /*
  * Sometimes we don't want to trace a function with the function