perf hists: Marking dummy hists entries

It does not make sense to make some computation (ratio, wdiff), when the
hist_entry is 'dummy' - added via hists__link.

Adding dummy field to struct hist_entry which indicates that it was
added by hists__link and avoiding some of the processing for such
entries.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-g8bxml0n0pnqsrpyd98p0ird@git.kernel.org


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