tracing: Move sleep-time and graph-time options out of the core trace_flags

The sleep-time and graph-time options are only for the function graph tracer
and are not used by anything else. As tracer options are now visible when
the tracer is not activated, its better to move the function graph specific
tracer options into the function graph tracer.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>