perf tools: sched-pipe bench: add (-n) nonblocking benchmark

perf tools: sched-pipe bench: add (-n) nonblocking benchmark

The -n mode will benchmark pipes in a non-blocking mode using
epoll_wait.

This specific mode was added to demonstrate the broken sync nature
of epoll: https://lore.kernel.org/lkml/20240426-zupfen-jahrzehnt-5be786bcdf04@brauner

Signed-off-by: Brian Geffon <bgeffon@google.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20241016190009.866615-1-bgeffon@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>