perf tools: Add 'cgroup-switches' software event

It counts how often cgroups are changed actually during the context
switches.

  # perf stat -a -e context-switches,cgroup-switches -a sleep 1

   Performance counter stats for 'system wide':

              11,267      context-switches
              10,950      cgroup-switches

         1.015634369 seconds time elapsed

Committer notes:

The kernel patches landed in v5.13, but this entry wasn't filled in
perf's parse-events tables, which was leading to a segfault when running
'perf list' on a kernel with that feature, as reported by Thomas
Richter.

Also removed the part touching tools/include/uapi/linux/perf_event.h as
it was updated in the usual sync with the kernel UAPI headers, in a
previous, already upstream, patch.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20210210083327.22726-3-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>