powerpc: Spinlock optimization and cleanup

This patch optimizes powerpc spinlock implementation by:

* Use the correct EH hint bit on the larx for supported ISA.  For lock
  acquisition, the thread that acquired the lock with a successful stcx
  does not want to give away the write ownership on the cacheline.  The
  idea is to make the load reservation "sticky" about retaining write
  authority to the line.  That way, the store that must inevitably come
  to release the lock can succeed quickly and not contend with other
  threads issuing lwarx.  If another thread does a store to the line
  (false sharing), the winning thread must give up write authority to
  the proper value of EH for the larx for a lock acquisition is 1.

* Increase contented lock performance by up to 40%, and no measurable
  impact on uncontended locks on P8.

Thanks to Adhemerval Zanella who did most of the work.  I've run some
tests, and addressed some minor feedback.

	* sysdeps/powerpc/nptl/pthread_spin_lock.c (pthread_spin_lock):
	Add lwarx hint, and use macro for acquire instruction.
	* sysdeps/powerpc/nptl/pthread_spin_trylock.c (pthread_spin_trylock):
	Likewise.
	* sysdep/unix/sysv/linux/powerpc/pthread_spin_unlock.c: Move to ...
	* sysdeps/powerpc/nptl/pthread_spin_unlock.c: ... here, and
	update to use new atomic macros.

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