x86, ioapic: Panic on irq-pin binding only if needed

Though the most time we are to panic on irq-pin allocation
fails, for PCI interrupts it's not the case and we could
continue operate even if irq-pin allocation failed.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20090805200931.GB5319@lenovo>
Signed-off-by: Ingo Molnar <mingo@elte.hu>