irq: for_each_irq_desc() move to irqnr.h

Impact: cleanup

before CONFIG_SPARSE_IRQ age, for_each_irq_desc() sat in irqnr.h and
could be called from generic code.

CONFIG_SPARSE_IRQ breaks this assumption, but SPARSE_IRQ version
for_each_irq_desc() also can move into irqnr.h easily.

Also, this patch unifies CONFIG_SPARSE_IRQ and !CONFIG_SPARSE_IRQ
for_each_irq_desc().

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 6492400..4db7d2d 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -203,7 +203,7 @@
 	return desc;
 }
 
-#else
+#else /* !CONFIG_SPARSE_IRQ */
 
 struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
 	[0 ... NR_IRQS-1] = {
@@ -218,7 +218,16 @@
 	}
 };
 
-#endif
+struct irq_desc *irq_to_desc(unsigned int irq)
+{
+	return (irq < NR_IRQS) ? irq_desc + irq : NULL;
+}
+
+struct irq_desc *irq_to_desc_alloc_cpu(unsigned int irq, int cpu)
+{
+	return irq_to_desc(irq);
+}
+#endif /* !CONFIG_SPARSE_IRQ */
 
 /*
  * What should we do if we get a hw irq event on an illegal vector?