handle "special" dma allocation in common code

[Christoph Hellwig]

Hi all,,

this series ensures that the common dma-direct code handles the somewhat
special allocation types requested by the DMA_ATTR_NON_CONSISTENT and
DMA_ATTR_NO_KERNEL_MAPPING flags directly.  To do so it also removes three
partial and thus broken implementations of DMA_ATTR_NON_CONSISTENT.  Last
but not least it switches arc to use the generic dma remapping code now
that arc doesn't implement any special behavior.