headers: smp_lock.h redux

* Remove smp_lock.h from files which don't need it (including some headers!)
* Add smp_lock.h to files which do need it
* Make smp_lock.h include conditional in hardirq.h
  It's needed only for one kernel_locked() usage which is under CONFIG_PREEMPT

  This will make hardirq.h inclusion cheaper for every PREEMPT=n config
  (which includes allmodconfig/allyesconfig, BTW)

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/mxser.c

@@ -23,6 +23,7 @@
 #include <linux/errno.h>
 #include <linux/signal.h>
 #include <linux/sched.h>
+#include <linux/smp_lock.h>
 #include <linux/timer.h>
 #include <linux/interrupt.h>
 #include <linux/tty.h>