lockref: include mutex.h rather than reinvent arch_mutex_cpu_relax

#include <linux/export.h>

#include <linux/lockref.h>

#include <linux/mutex.h>

#if USE_CMPXCHG_LOCKREF

# define cmpxchg64_relaxed cmpxchg64

#endif

/*

 * Allow architectures to override the default cpu_relax() within CMPXCHG_LOOP.

 * This is useful for architectures with an expensive cpu_relax().

 */

#ifndef arch_mutex_cpu_relax

# define arch_mutex_cpu_relax() cpu_relax()

#endif

/*

 * Note that the "cmpxchg()" reloads the "old" value for the

 * failure case.