perf hists browser: Allow annotating entries in callchains

perf hists browser: Allow annotating entries in callchains

Instead of annotating just the top level hist_entry, allow instead
annotating a map_symbol, i.e. the top level hist_entry or one of the
callchains for which there were samples.

Suggested-by: Stephane Eranian <eranian@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-k1zxj5564je9jei4yd15ouwn@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>