perf tools: Introduce struct map_symbol

That will be in both struct hist_entry and struct
callchain_list, so that the TUI can store a pointer to the pair
(map, symbol) in the trees where hist_entries and
callchain_lists are present, to allow precise annotation instead
of looking for the first symbol with the selected name.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1269459619-982-4-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>