perf evsel: Add evsel__clone() function

perf evsel: Add evsel__clone() function

The evsel__clone() is to create an exactly same evsel from same
attributes.  The function assumes the given evsel is not configured
yet so it cares fields set during event parsing.  Those fields are now
moved together as Jiri suggested.  Note that metric events will be
handled by later patch.

It will be used by perf stat to generate separate events for each
cgroup.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200924124455.336326-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>