x86, perf: Add power_end event to process_*.c cpu_idle routine

Systems using the idle thread from process_32.c and process_64.c
do not generate power_end events which could be traced using
perf. This patch adds the event generation for such systems.

Signed-off-by: Robert Schoene <robert.schoene@tu-dresden.de>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1276515440.5441.45.camel@localhost>
Signed-off-by: Ingo Molnar <mingo@elte.hu>