x86, perf_event: Rename 'performance counter interrupt'

In 'cdd6c482

', we renamed
Performance Counters -> Performance Events.

The name showed up in /proc/interrupts also needs a change. I use
PMI (Performance monitoring interrupt) here, since it is the
official name used in Intel's documents.

Signed-off-by: Li Hong <lihong.hi@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091014105039.GA22670@uhli>
Signed-off-by: Ingo Molnar <mingo@elte.hu>