selftests/perf_events: Add a SIGTRAP stress test with disables

Add a SIGTRAP stress test that exercises repeatedly enabling/disabling
an event while it concurrently keeps firing.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/Y0E3uG7jOywn7vy3@elver.google.com/