x86: use nr_irqs

also add first_free_entry and pin_map_size, which were NR_IRQS derived
constants.

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

arch/x86/kernel/irqinit_64.c

@@ -142,7 +142,7 @@ void __init init_ISA_irqs(void)
 	init_bsp_APIC();
 	init_8259A(0);
 
-	for (i = 0; i < NR_IRQS; i++) {
+	for (i = 0; i < nr_irqs; i++) {
 		irq_desc[i].status = IRQ_DISABLED;
 		irq_desc[i].action = NULL;
 		irq_desc[i].depth = 1;