compat: backport sg_alloc_table_from_pages() from efc42bc9

compat: backport sg_alloc_table_from_pages() from efc42bc9

This backports sg_alloc_table_from_pages() added via commit efc42bc9

mcgrof@frijol ~/linux-next (git::master)$ git describe --contains efc42bc9
v3.6-rc1~57^2~11

commit efc42bc98058a36d761b16a114823db1a902ed05
Author: Tomasz Stanislawski <t.stanislaws@samsung.com>
Date:   Mon Jun 18 09:25:01 2012 +0200

    scatterlist: add sg_alloc_table_from_pages function

    This patch adds a new constructor for an sg table. The table is constructed
    from an array of struct pages. All contiguous chunks of the pages are merged
    into a single sg nodes. A user may provide an offset and a size of a buffer if
    the buffer is not page-aligned.

    The function is dedicated for DMABUF exporters which often perform conversion
    from an page array to a scatterlist. Moreover the scatterlist should be
    squashed in order to save memory and to speed-up the process of DMA mapping
    using dma_map_sg.

    The code is based on the patch 'v4l: vb2-dma-contig: add support for
    scatterlist in userptr mode' and hints from Laurent Pinchart.

    Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
    Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
    Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>