tracing: Convert some power events to DEFINE_EVENT

Use DECLARE_EVENT_CLASS to remove duplicate code:

   text    data     bss     dec     hex filename
   4312     524      12    4848    12f0 kernel/trace/power-traces.o.old
   3455     524       8    3987     f93 kernel/trace/power-traces.o

Two events are converted:

  power: power_start, power_frequency

No change in functionality.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>
LKML-Reference: <4B0E28C2.1090906@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>