perf annotate: Display total number of samples with --show-total-period

To compare two records on an instruction base, with --show-total-period
option provided, display total number of samples that belong to a line
in assembly language.

New hot key 't' is introduced for 'perf annotate' TUI.

Signed-off-by: Martin Liska <mliska@suse.cz>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/5583E26D.1040407@suse.cz
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>