ftrace: rename iter_ctrl to trace_options

Impact: rename file /debug/tracing/iter_ctrl to /debug/tracing/trace_options

The original ftrace had a file called "iter_ctrl" that would control
the way the output was iterated. But this file grew into a catch all
for different trace options. This patch renames the file from iter_ctrl
to trace_options to reflect this change.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>