perf sched: Determine the number of CPUs automatically

For 'perf sched map' output, determine max_cpu automatically,
instead of the static default of 15.

[ v2: use sysconf() pointed out by Arjan van de Ven <arjan@infradead.org> ]

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>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>