locking,arch,mips: Fold atomic_ops

Many of the atomic op implementations are the same except for one
instruction; fold the lot into a few CPP macros and reduce LoC.

This also prepares for easy addition of new ops.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maciej W. Rozycki <macro@codesourcery.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Link: http://lkml.kernel.org/r/20140508135852.521548500@infradead.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>