sparse irqs: handle !GENIRQ platforms

Impact: build fix

fix:

 In file included from /home/mingo/tip/arch/m68k/amiga/amiints.c:39:
 /home/mingo/tip/include/linux/interrupt.h:21: error: expected identifier or '('
 /home/mingo/tip/arch/m68k/amiga/amiints.c: In function 'amiga_init_IRQ':

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/irqnr.h b/include/linux/irqnr.h
index 13754f8..95d2b74 100644
--- a/include/linux/irqnr.h
+++ b/include/linux/irqnr.h
@@ -1,6 +1,11 @@
 #ifndef _LINUX_IRQNR_H
 #define _LINUX_IRQNR_H
 
+/*
+ * Generic irq_desc iterators:
+ */
+#ifdef __KERNEL__
+
 #ifndef CONFIG_GENERIC_HARDIRQS
 #include <asm/irq.h>
 # define nr_irqs		NR_IRQS
@@ -11,10 +16,12 @@
 # define for_each_irq_desc_reverse(irq, desc)                          \
 	for (irq = nr_irqs - 1; irq >= 0; irq--)
 #else
+
+extern int nr_irqs;
+
 #ifndef CONFIG_SPARSE_IRQ
 
 struct irq_desc;
-extern int nr_irqs;
 # define for_each_irq_desc(irq, desc)		\
 	for (irq = 0, desc = irq_desc; irq < nr_irqs; irq++, desc++)
 # define for_each_irq_desc_reverse(irq, desc)                          \
@@ -26,4 +33,6 @@
 #define for_each_irq_nr(irq)                   \
        for (irq = 0; irq < nr_irqs; irq++)
 
+#endif /* __KERNEL__ */
+
 #endif