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/interrupt.h b/include/linux/interrupt.h
index 79e915e..777f89e 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -14,12 +14,12 @@
 #include <linux/irqflags.h>
 #include <linux/smp.h>
 #include <linux/percpu.h>
+#include <linux/irqnr.h>
+
 #include <asm/atomic.h>
 #include <asm/ptrace.h>
 #include <asm/system.h>
 
-extern int nr_irqs;
-
 /*
  * These correspond to the IORESOURCE_IRQ_* defines in
  * linux/ioport.h to select the interrupt line behaviour.  When