perf tools: Create util/sort.and use it

Create util/sort.[ch] and move common functionality for
builtin-report.c and builtin-annotate.c there, and make use of it.

Signed-off-by: John Kacur <jkacur@redhat.com>
LKML-Reference: <alpine.LFD.2.00.0909241758390.11383@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>