genirq: Move kstat_incr_irqs_this_cpu() to core

No more users outside the core code. Put it into the poison
cabinet. That also gets rid of the linux/irq.h include in
kernel_stat.h

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140223212739.124207133@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --cc include/linux/kernel_stat.h
Simple merge

diff --cc kernel/irq/internals.h
Simple merge