tools include UAPI: Sync linux/sched.h copy with the kernel sources

tools include UAPI: Sync linux/sched.h copy with the kernel sources

Picking the changes from:

  f0e1a0643a59bf1f ("sched_ext: Implement BPF extensible scheduler class")

The inclusion of the SCHED_EXT define doesn't cause any change in
behaviour in tools/perf.

This just silences this perf tools build warning:

  diff -u tools/perf/trace/beauty/include/uapi/sound/asound.h include/uapi/sound/asound.h

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/lkml/ZvrDShNVXotZpiwk@x1
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>