fix a layering violation in videobuf2 and improve dma_map_resource v2

[Christoph Hellwig]

On Fri, Feb 01, 2019 at 08:05:21AM +0100, Marek Szyprowski wrote:
> Works fine on older Exynos based boards with IOMMU and CMA disabled.
> 
> Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>

Thanks.  I've merged the ѕeries into the dma-mapping tree, and I've
also made a stable branch available at:

    git://git.infradead.org/users/hch/dma-mapping.git videobuf-map-resource

in case it needs to be pulled into the media tree.