asm-generic/irqstat: Add optional __nmi_count member

Add an optional __nmi_count member to irq_cpustat_t so more architectures
can use the generic version.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20201113141733.501611990@linutronix.de

include/asm-generic/hardirq.h

@@ -7,6 +7,9 @@
 
 typedef struct {
 	unsigned int __softirq_pending;
+#ifdef ARCH_WANTS_NMI_IRQSTAT
+	unsigned int __nmi_count;
+#endif
 } ____cacheline_aligned irq_cpustat_t;
 
 #include <linux/irq_cpustat.h>	/* Standard mappings for irq_cpustat_t above */