dmaengine maintainer update

I am stepping down as dmaengine maintainer as the bulk of the activity
in the subsystem is primarily targeted at the slave-dma case handled by
Vinod, and I have recently been unable to give the few patches I do
receive timely review.  There is still an item in my backlog to
eliminate the async_tx api and the constraints it poses on dmaengine
drivers, but I need not hold on to the maintainer role in the meantime.
I will still be subscribed to dmaengine@vger.kernel.org to answer
questions, but all patches should be routed through Vinod unless/until a
maintainer for the non-slave-dma use case arrives.  It is non-entirely
clear at this point that there is enough work going forward for a
separate maintainer of the pure-offload case.

Ongoing development of the ioatdma driver is handled by Dave.  I'm still
interested in reviewing ioatdma patches, but he is the primary
maintainer/developer going forward.

IOP platforms are not generating any traffic in my inbox, but if a patch
did arrive I've long since lost access to hardware.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>