perf sort: Make column width code per hists instance

They were globals, and since we support multiple hists and sessions
at the same time, it doesn't make sense to calculate those values
considereing all symbols in all sessions.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.h

@@ -146,6 +146,8 @@ struct dso *dso__new(const char *name);
 struct dso *dso__new_kernel(const char *name);
 void dso__delete(struct dso *self);
 
+int dso__name_len(const struct dso *self);
+
 bool dso__loaded(const struct dso *self, enum map_type type);
 bool dso__sorted_by_name(const struct dso *self, enum map_type type);