powerpc: Add timer, performance monitor and machine check counts to /proc/interrupts

With NO_HZ it is useful to know how often the decrementer is going off. The
patch below adds an entry for it and also adds it into the /proc/stat
summaries.

While here, I added performance monitoring and machine check exceptions.
I found it useful to keep an eye on the PMU exception rate
when using the perf tool. Since it's possible to take a completely
handled machine check on a System p box it also sounds like a good idea to
keep a machine check summary.

The event naming matches x86 to keep gratuitous differences to a minimum.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/time.c

@@ -575,6 +575,8 @@ void timer_interrupt(struct pt_regs * regs)
 
 	trace_timer_interrupt_entry(regs);
 
+	__get_cpu_var(irq_stat).timer_irqs++;
+
 	/* Ensure a positive value is written to the decrementer, or else
 	 * some CPUs will continuue to take decrementer exceptions */
 	set_dec(DECREMENTER_MAX);