clean up and modularize arch dma_mapping interface

[David Miller]

From: Christoph Hellwig <hch at lst.de>
Date: Thu,  8 Jun 2017 15:25:25 +0200

> for a while we have a generic implementation of the dma mapping routines
> that call into per-arch or per-device operations.  But right now there
> still are various bits in the interfaces where don't clearly operate
> on these ops.  This series tries to clean up a lot of those (but not all
> yet, but the series is big enough).  It gets rid of the DMA_ERROR_CODE
> way of signaling failures of the mapping routines from the
> implementations to the generic code (and cleans up various drivers that
> were incorrectly using it), and gets rid of the ->set_dma_mask routine
> in favor of relying on the ->dma_capable method that can be used in
> the same way, but which requires less code duplication.

There is unlikely to be conflicts for the sparc and net changes, so I
will simply ACK them.

Thanks Christoph.