genirq: Add a kstat helper to increment irq stats

There is a common pattern all over the place:

      kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));

This results in a call to core code anyway. So provide a function
which does the same thing in core.

While at it, replace the butt ugly macro with an inline.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140223212737.422068876@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/irqdesc.c

@@ -489,6 +489,11 @@ void dynamic_irq_cleanup(unsigned int irq)
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 }
 
+void kstat_incr_irq_this_cpu(unsigned int irq)
+{
+	kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
+}
+
 unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
 {
 	struct irq_desc *desc = irq_to_desc(irq);