ftrace: Introduce struct ftrace_graph_data

The struct ftrace_graph_data is for generalizing the access to
set_graph_function file.  This is a preparation for adding support to
set_graph_notrace.

Link: http://lkml.kernel.org/r/1381739066-7531-3-git-send-email-namhyung@kernel.org



Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>