Mutex: Add pthread mutex tunables

This patch does not have any functionality change, we only provide a spin
count tunes for pthread adaptive spin mutex. The tunable
glibc.pthread.mutex_spin_count tunes can be used by system administrator to
squeeze system performance according to different hardware capabilities and
workload characteristics.

The maximum value of spin count is limited to 32767 to avoid the overflow
of mutex->__data.__spins variable with the possible type of short in
pthread_mutex_lock ().

The default value of spin count is set to 100 with the reference to the
previous number of times of spinning via trylock. This value would be
architecture-specific and can be tuned with kinds of benchmarks to fit most
cases in future.

I would extend my appreciation sincerely to H.J.Lu for his help to refine
this patch series.

	* manual/tunables.texi (POSIX Thread Tunables): New node.
	* nptl/Makefile (libpthread-routines): Add pthread_mutex_conf.
	* nptl/nptl-init.c: Include pthread_mutex_conf.h
	(__pthread_initialize_minimal_internal) [HAVE_TUNABLES]: Call
	 __pthread_tunables_init.
	* nptl/pthreadP.h (MAX_ADAPTIVE_COUNT): Remove.
	(max_adaptive_count): Define.
	* nptl/pthread_mutex_conf.c: New file.
	* nptl/pthread_mutex_conf.h: New file.
	* sysdeps/generic/adaptive_spin_count.h: New file.
	* sysdeps/nptl/dl-tunables.list: New file.
	* nptl/pthread_mutex_lock.c (__pthread_mutex_lock): Use
	max_adaptive_count () not MAX_ADAPTIVE_COUNT.
	* nptl/pthread_mutex_timedlock.c (__pthrad_mutex_timedlock):
	Likewise.

Suggested-by: Andi Kleen <andi.kleen@intel.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Signed-off-by: Kemi.wang <kemi.wang@intel.com>