Re: cleanup the dma_pgprot handling v2

I've pulled this into the dma-mapping for-next tree now.

cleanup the dma_pgprot handling v2

Hi all, this series replaces the arch_dma_mmap_pgprot hooks with the simpler pgprot_dmacoherent as used by the arm code already and cleans up various bits around that area. Changes since v1: - improve the new arm64 comment - keep the special DMA_ATTR_WRITE_COMBINE handling for mips and docum