tracing: Make tracing_cpumask available for all instances

Allow tracer instances to disable tracing by cpu by moving
the static global tracing_cpumask into trace_array.

Link: http://lkml.kernel.org/r/921622317f239bfc2283cac2242647801ef584f2.1375980149.git.azl@google.com

Cc: Vaibhav Nagarnaik <vnagarnaik@google.com>
Cc: David Sharp <dhsharp@google.com>
Cc: Alexander Z Lam <lambchop468@gmail.com>
Signed-off-by: Alexander Z Lam <azl@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index afaae41..502fed7 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -206,6 +206,7 @@
 	struct dentry		*event_dir;
 	struct list_head	systems;
 	struct list_head	events;
+	cpumask_var_t		tracing_cpumask; /* only trace on set CPUs */
 	int			ref;
 };