Fix build failure due to hwirq.h needing smp_lock.h

Arnd Bergmann did an automated scripting run to find left-over instances
of <linux/smp_lock.h>, and had made it trigger it on the normal BKL use
of lock_kernel and unlock_lernel (and apparently release_kernel_lock and
reacquire_kernel_lock too, used by the scheduler).

That resulted in commit 451a3c24b013 ("BKL: remove extraneous #include
<smp_lock.h>").

However, hardirq.h was the only remaining user of the old
'kernel_locked()' interface, and Arnd's script hadn't checked for that.
So depending on your configuration and what header files had been
included, you would get errors like "implicit declaration of function
'kernel_locked'" during the build.

The right fix is not to just re-instate the smp_lock.h include - it is
to just remove 'kernel_locked()' entirely, since the only use was this
one special low-level detail. Just make hardirq.h do it directly.

In fact this simplifies and clarifies the code, because some trivial
analysis makes it clear that hardirq.h only ever used _one_ of the two
definitions of kernel_locked(), so we can remove the other one entirely.

Reported-by: Zimny Lech <[e-mail]>
Reported-and-acked-by: Randy Dunlap <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/hardirq.h

···
 #define in_nmi()	(preempt_count() & NMI_MASK)
 
 #if defined(CONFIG_PREEMPT) && defined(CONFIG_BKL)
-# define PREEMPT_INATOMIC_BASE kernel_locked()
+# define PREEMPT_INATOMIC_BASE (current->lock_depth >= 0)
 #else
 # define PREEMPT_INATOMIC_BASE 0
 #endif

include/linux/smp_lock.h

···
 #ifdef CONFIG_LOCK_KERNEL
 #include <linux/sched.h>
 
-#define kernel_locked()		(current->lock_depth >= 0)
-
 extern int __lockfunc __reacquire_kernel_lock(void);
 extern void __lockfunc __release_kernel_lock(void);
 
···
 #define lock_kernel()
 #define unlock_kernel()
 #define cycle_kernel_lock()			do { } while(0)
-#define kernel_locked()				1
 #endif /* CONFIG_BKL */
 
 #define release_kernel_lock(task)		do { } while(0)