x86: make 32 bit to use sparse_irq

but actually irq still needs to be less than NR_IRQS, because
interrupt[NR_IRQS] in entry.S.

need to enable per_cpu vector...

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>