libperf: Add a test case for read formats

libperf: Add a test case for read formats

It checks a various combination of the read format settings and verify
it return the value in a proper position.  The test uses task-clock
software events to guarantee it's always active and sets enabled/running
time.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220819003644.508916-4-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>