s390: Avoid call to irq_reserve_irqs()

There is no need to mark the lower interrupts as reserved in order to
exclude them from dynamic allocation.

Provide arch_dynirq_lower_bound() to exclude the lower space.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux390@de.ibm.com
Link: http://lkml.kernel.org/r/20140507154339.811205235@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/s390/kernel/irq.c

@@ -92,7 +92,6 @@ static const struct irq_class irqclass_sub_desc[NR_ARCH_IRQS] = {
 
 void __init init_IRQ(void)
 {
-	irq_reserve_irqs(0, THIN_INTERRUPT);
 	init_cio_interrupts();
 	init_airq_interrupts();
 	init_ext_interrupts();
@@ -151,6 +150,11 @@ out:
 	return 0;
 }
 
+unsigned int arch_dynirq_lower_bound(unsigned int from)
+{
+	return from < THIN_INTERRUPT ? THIN_INTERRUPT : from;
+}
+
 /*
  * Switch to the asynchronous interrupt stack for softirq execution.
  */