Remove compilation failure when ftrace in enabled.

Error log:
  CC      kernel/trace/power-traces.o
In file included from arch/microblaze/include/asm/irq.h:15,
                 from include/linux/irq.h:27,
                 from include/asm-generic/hardirq.h:12,
                 from arch/microblaze/include/asm/hardirq.h:15,
                 from include/linux/hardirq.h:7,
                 from include/linux/ftrace_event.h:7,
                 from include/trace/ftrace.h:19,
                 from include/trace/define_trace.h:96,
                 from include/trace/events/power.h:240,
                 from kernel/trace/power-traces.c:14:
include/linux/interrupt.h: In function '__raise_softirq_irqoff':
include/linux/interrupt.h:413: error: implicit declaration of function 'trace_softirq_raise'
In file included from include/trace/ftrace.h:554,
                 from include/trace/define_trace.h:96,
                 from include/trace/events/power.h:240,
                 from kernel/trace/power-traces.c:14:
include/trace/events/irq.h: In function 'ftrace_test_probe_irq_handler_entry':
include/trace/events/irq.h:37: error: implicit declaration of function 'check_trace_callback_type_irq_handler_entry'
include/trace/events/irq.h: In function 'ftrace_test_probe_irq_handler_exit':
include/trace/events/irq.h:67: error: implicit declaration of function 'check_trace_callback_type_irq_handler_exit'
include/trace/events/irq.h: In function 'ftrace_test_probe_softirq_entry':
include/trace/events/irq.h:112: error: implicit declaration of function 'check_trace_callback_type_softirq_entry'
include/trace/events/irq.h: In function 'ftrace_test_probe_softirq_exit':
include/trace/events/irq.h:126: error: implicit declaration of function 'check_trace_callback_type_softirq_exit'
include/trace/events/irq.h: In function 'ftrace_test_probe_softirq_raise':
include/trace/events/irq.h:140: error: implicit declaration of function 'check_trace_callback_type_softirq_raise'
make[5]: *** [kernel/trace/power-traces.o] Error 1
make[4]: *** [kernel/trace] Error 2
make[3]: *** [kernel] Error 2
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Michal Simek <monstr@monstr.eu>