x86: move kstat_irqs from kstat to irq_desc

based on Eric's patch ...

together mold it with dyn_array for irq_desc, will allcate kstat_irqs for
nr_irq_desc alltogether if needed. -- at that point nr_cpus is known already.

v2: make sure system without generic_hardirqs works they don't have irq_desc
v3: fix merging
v4: [mingo@elte.hu] fix typo

[ mingo@elte.hu ] irq: build fix

fix:

 arch/x86/xen/spinlock.c: In function 'xen_spin_lock_slow':
 arch/x86/xen/spinlock.c:90: error: 'struct kernel_stat' has no member named 'irqs'

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 60c856a..cbf471a 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -158,6 +158,11 @@
 	struct irq_desc		*next;
 	struct timer_rand_state *timer_rand_state;
 #endif
+#ifdef CONFIG_HAVE_DYN_ARRAY
+	unsigned int            *kstat_irqs;
+#else
+	unsigned int            kstat_irqs[NR_CPUS];
+#endif
 	irq_flow_handler_t	handle_irq;
 	struct irq_chip		*chip;
 	struct msi_desc		*msi_desc;
@@ -190,6 +195,8 @@
 /* could be removed if we get rid of all irq_desc reference */
 extern struct irq_desc irq_desc[NR_IRQS];
 #endif
+#define kstat_irqs_this_cpu(DESC) \
+	((DESC)->kstat_irqs[smp_processor_id()])
 
 /*
  * Migration helpers for obsolete names, they will go away: