tracing: Fix event header migrate.h to include tracepoint.h

The trace event headers are required to include tracepoint.h. The only reason
they worked now is because module.h included tracepoint.h, and that will soon
change.

Link: http://lkml.kernel.org/r/20140226190644.591040764@goodmis.org



Fixes: 7b2a2d4a "mm: migrate: Add a tracepoint for migrate_pages"
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>