of: clean-up ifdefs in of_irq.h

Much of of_irq.h is needlessly ifdef'ed. Clean this up and minimize the
amount ifdef'ed code. This fixes some  build warnings when CONFIG_OF
is not enabled (seen on i386 and x86_64):

include/linux/of_irq.h:82:7: warning: 'struct device_node' declared inside parameter list [enabled by default]
include/linux/of_irq.h:82:7: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]
include/linux/of_irq.h:87:47: warning: 'struct device_node' declared inside parameter list [enabled by default]

Compile tested on i386, sparc and arm.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

include/linux/of_irq.h

 #ifndef __OF_IRQ_H
 #define __OF_IRQ_H
 
-#if defined(CONFIG_OF)
-struct of_irq;
 #include <linux/types.h>
 #include <linux/errno.h>
 #include <linux/irq.h>
@@ -10,14 +8,6 @@ struct of_irq;
 #include <linux/ioport.h>
 #include <linux/of.h>
 
-/*
- * irq_of_parse_and_map() is used by all OF enabled platforms; but SPARC
- * implements it differently.  However, the prototype is the same for all,
- * so declare it here regardless of the CONFIG_OF_IRQ setting.
- */
-extern unsigned int irq_of_parse_and_map(struct device_node *node, int index);
-
-#if defined(CONFIG_OF_IRQ)
 /**
  * of_irq - container for device_node/irq_specifier pair for an irq controller
  * @controller: pointer to interrupt controller device tree node
@@ -71,11 +61,17 @@ extern int of_irq_to_resource(struct device_node *dev, int index,
 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 struct device_node *of_irq_find_parent(struct device_node *child);
 
 extern void of_irq_init(const struct of_device_id *matches);
 
-#endif /* CONFIG_OF_IRQ */
+#if defined(CONFIG_OF)
+/*
+ * irq_of_parse_and_map() is used by all OF enabled platforms; but SPARC
+ * implements it differently.  However, the prototype is the same for all,
+ * so declare it here regardless of the CONFIG_OF_IRQ setting.
+ */
+extern unsigned int irq_of_parse_and_map(struct device_node *node, int index);
+extern struct device_node *of_irq_find_parent(struct device_node *child);
 
 #else /* !CONFIG_OF */
 static inline unsigned int irq_of_parse_and_map(struct device_node *dev,