locking/lockdep: Reduce header dependencies in <linux/debug_locks.h>

The inclusion of printk.h leads to a circular dependency if spinlock_t is
based on rtmutexes on RT enabled kernels.

Include only atomic.h (xchg()) and cache.h (__read_mostly) which is all
what debug_locks.h requires.

Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Sebastian Andrzej Siewior

include/linux/debug_locks.h

@@ -3,8 +3,7 @@
 #define __LINUX_DEBUG_LOCKING_H
 
 #include <linux/atomic.h>
-#include <linux/bug.h>
-#include <linux/printk.h>
+#include <linux/cache.h>
 
 struct task_struct;