tracing, power-trace: make it build even if the power-tracer is turned off

Impact: build fix

The 'struct power_trace' definition is needed (for the event tracer) even if
the power-tracer plugin is turned off in the .config.

Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <20090306104106.GF31042@elte.hu>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/trace/power.h

@@ -11,12 +11,10 @@ enum {
 };
 
 struct power_trace {
-#ifdef CONFIG_POWER_TRACER
 	ktime_t			stamp;
 	ktime_t			end;
 	int			type;
 	int			state;
-#endif
 };
 
 DECLARE_TRACE(power_start,