perf list: Fix large list output by using the pager

When /sys/kernel/debug is mounted the list can be imense, so
use the pager like the other tools.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090812174459.GB3495@ghostprotocols.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>