libtracefs: Unit test for iterate over raw events in sorted order

Enhanced the unit test of tracefs_iterate_raw_events() API to check if
events are iterated in sorted order: latest first. Added a check for the
correct CPU number in the record, passed to the callback.

Link: https://lore.kernel.org/linux-trace-devel/20210407034822.2373958-3-tz.stoyanov@gmail.com

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>