perf hists: Replace perf_evsel arg perf_hpp_fmt's header callback

perf hists: Replace perf_evsel arg perf_hpp_fmt's header callback

Replacing perf_evsel arg perf_hpp_fmt's header callback with hists
object.

None of the actual callbacks actually use evsel object, also this will
be helpful in future for non evsel related hist browsers.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1465928361-2442-10-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>