The CPU hotplug callbacks are not covered by lockdep versus the cpu hotplug
rwsem.

CPU0						CPU1
cpuhp_setup_state(STATE, startup, teardown);
 cpus_read_lock();
  invoke_callback_on_ap();
    kick_hotplug_thread(ap);
    wait_for_completion();			hotplug_thread_fn()
    						  lock(m);
						  do_stuff();
						  unlock(m);

Lockdep does not know about this dependency and will not trigger on the
following code sequence:

	  lock(m);
	  cpus_read_lock();
	  
Add a lockdep map and connect the initiators lock chain with the hotplug
thread lock chain, so potential deadlocks can be detected.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Siewior <bigeasy@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170524081549.709375845@linutronix.de