x86: Distinguish TLB shootdown interrupts from other functions call interrupts

As TLB shootdown requests to other CPU cores are now using function call
interrupts, TLB shootdowns entry in /proc/interrupts is always shown as 0.

This behavior change was introduced by commit 52aec3308d ("x86/tlb:
replace INVALIDATE_TLB_VECTOR by CALL_FUNCTION_VECTOR").

This patch reverts TLB shootdowns entry in /proc/interrupts to count TLB
shootdowns separately from the other function call interrupts.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Link: http://lkml.kernel.org/r/20120926021128.22212.20440.stgit@hpxw
Acked-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/mm/tlb.c

@@ -98,6 +98,8 @@ static void flush_tlb_func(void *info)
 {
 	struct flush_tlb_info *f = info;
 
+	inc_irq_stat(irq_tlb_count);
+
 	if (f->flush_mm != this_cpu_read(cpu_tlbstate.active_mm))
 		return;