locking,arch,xtensa: 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: Chris Zankel <chris@zankel.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linux-xtensa@linux-xtensa.org
Link: http://lkml.kernel.org/r/20140508135852.879575796@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>