use generic DMA mapping code in powerpc V3

[Christoph Hellwig]

Hi all,

this series switches the powerpc port to use the generic swiotlb and
noncoherent dma ops, and to use more generic code for the coherent
direct mapping, as well as removing a lot of dead code.

The changes since v1 are to big to list and v2 was not posted in public.

As this series is very large and depends on the dma-mapping tree I've
also published a git tree:

    git://git.infradead.org/users/hch/misc.git powerpc-dma.3

Gitweb:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/powerpc-dma.3