dt/irq: add empty of_irq_count for !OF_IRQ

Add an empty version of of_irq_count for !OF_IRQ. This fixes build error
on sparc in linux-next:

drivers/gpio/gpio-bcm-kona.c:542: undefined reference to `of_irq_count'

Signed-off-by: Rob Herring <rob.herring@calxeda.com>

include/linux/of_irq.h

@@ -37,12 +37,20 @@ extern int of_irq_parse_one(struct device_node *device, int index,
 extern unsigned int irq_create_of_mapping(struct of_phandle_args *irq_data);
 extern int of_irq_to_resource(struct device_node *dev, int index,
 			      struct resource *r);
-extern int of_irq_count(struct device_node *dev);
 extern int of_irq_to_resource_table(struct device_node *dev,
 		struct resource *res, int nr_irqs);
 
 extern void of_irq_init(const struct of_device_id *matches);
 
+#ifdef CONFIG_OF_IRQ
+extern int of_irq_count(struct device_node *dev);
+#else
+static inline int of_irq_count(struct device_node *dev)
+{
+	return 0;
+}
+#endif
+
 #if defined(CONFIG_OF)
 /*
  * irq_of_parse_and_map() is used by all OF enabled platforms; but SPARC