tracing: Allow tracers to start at core initcall

There's times during debugging that it is helpful to see traces of early
boot functions. But the tracers are initialized at device_initcall()
which is quite late during the boot process. Setting the kernel command
line parameter ftrace=function will not show anything until the function
tracer is initialized. This prevents being able to trace functions before
device_initcall().

There's no reason that the tracers need to be initialized so late in the
boot process. Move them up to core_initcall() as they still need to come
after early_initcall() which initializes the tracing buffers.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_functions_graph.c

@@ -1474,4 +1474,4 @@ static __init int init_graph_trace(void)
 	return register_tracer(&graph_trace);
 }
 
-device_initcall(init_graph_trace);
+core_initcall(init_graph_trace);