locking/atomic: Introduce inc/dec variants for the atomic_fetch_$op() API

With the inclusion of atomic FETCH-OP variants, many places in the
kernel can make use of atomic_fetch_$op() to avoid the callers that
need to compute the value/state _before_ the operation.

Peter Zijlstra laid out the machinery but we are still missing the
simpler dec,inc() calls (which future patches will make use of).

This patch only deals with the generic code, as at least right now
no arch actually implement them -- which is similar to what the
OP-RETURN primitives currently do.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: James.Bottomley@HansenPartnership.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: awalls@md.metrocast.net
Cc: bp@alien8.de
Cc: cw00.choi@samsung.com
Cc: davem@davemloft.net
Cc: dledford@redhat.com
Cc: dougthompson@xmission.com
Cc: gregkh@linuxfoundation.org
Cc: hans.verkuil@cisco.com
Cc: heiko.carstens@de.ibm.com
Cc: jikos@kernel.org
Cc: kys@microsoft.com
Cc: mchehab@osg.samsung.com
Cc: pfg@sgi.com
Cc: schwidefsky@de.ibm.com
Cc: sean.hefty@intel.com
Cc: sumit.semwal@linaro.org
Link: http://lkml.kernel.org/r/20160628215651.GA20048@linux-80c1.suse


Signed-off-by: Ingo Molnar <mingo@kernel.org>