perf hists browser: Introduce struct hist_browser title callback

perf hists browser: Introduce struct hist_browser title callback

We can now setup title callback for hist_browser, which will be useful
in following changes to create customized hist_browsers.

This also separates struct perf_evsel dependency out of hist_browser
basic code.

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/1466459899-1166-5-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>