tools/sched_ext: Sync with scx repo

Synchronize with https://github.com/sched-ext/scx

 at d384453984a0 ("kernel:
Sync at ad3b301a ("sched_ext: Provides a sysfs 'events' to expose core
event counters")").

Signed-off-by: Tejun Heo <tj@kernel.org>