perf hists browser: Offer 'Zoom into DSO'/'Map details' only when sort order has...

perf hists browser: Offer 'Zoom into DSO'/'Map details' only when sort order has 'dso'

We can't offer a zoom into DSO when a bucket (struct hist_entry) may
have samples for more than one DSO, i.e. when 'dso' is not part of
the sort order, ditto for 'Map details', fix it.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>,
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1452960197-5323-9-git-send-email-namhyung@kernel.org
[ Carved out from a  larger patch, moved check to add_{dso,map}_opt() ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>