x86, ioapic: Introduce for_each_irq_pin() helper

This allow us to save a few lines of code.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: yinghai@kernel.org
LKML-Reference: <20090801075435.597863129@openvz.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>