consolidate swiotlb dma_map implementations

[Christoph Hellwig]

A lot of architectures have essentially identical dma_map_ops
implementations to use swiotlb.  This series adds new generic
swiotlb_alloc/free helpers that take the attrs argument exposed
in dma_map_ops, and which do an enhanced direct allocation
modelled after x86 and reused from the dma-direct code, and
then switches most architectures over to it.  The only exceptions
are mips, which requires additional cache flushing which will
need a new abstraction, and x86 itself which will be handled in
a later series with other x86 dma mapping changes.

To support the generic code a few architectures that currently
use ZONE_DMA/GFP_DMA for <= 32-bit allocations are switched to
implement ZONE_DMA32 instead.

This series is based on the previously sent series to consolidate
the direct dma mapping implementation.  A git tree with this
series as well as the prerequisites is available here:

   git://git.infradead.org/users/hch/misc.git swiotlb

Gitweb:

   http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/swiotlb