selftests/perf_events: Test FASYNC with watermark wakeups

The test uses PERF_RECORD_SWITCH records to fill the ring buffer and
trigger the watermark wakeup, which in turn should trigger an IO
signal.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240413141618.4160-4-khuey@kylehuey.com