perf_counter tools: Prepare for 'perf annotate'

Prepare for the 'perf annotate' implementation by splitting off
builtin-annotate.c from builtin-report.c.

( We keep this commit separate to ease the later librarization
  of the facilities that perf-report and perf-annotate shares. )

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>