compat: backport sg page iterator a321e91b

compat: backport sg page iterator a321e91b

This backports commit a321e91b which adds the
scatterlist simple page iterator.

mcgrof@frijol ~/linux-next (git::master)$ git describe --contains a321e91b
v3.9-rc1~46^2~149

commit a321e91b6d73ed011ffceed384c40d2785cf723b
Author: Imre Deak <imre.deak@intel.com>
Date:   Wed Feb 27 17:02:56 2013 -0800

    lib/scatterlist: add simple page iterator

    Add an iterator to walk through a scatter list a page at a time starting
    at a specific page offset.  As opposed to the mapping iterator this is
    meant to be small, performing well even in simple loops like collecting
    all pages on the scatterlist into an array or setting up an iommu table
    based on the pages' DMA address.

    Signed-off-by: Imre Deak <imre.deak@intel.com>
    Cc: Maxim Levitsky <maximlevitsky@gmail.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
    Tested-by: Stephen Warren <swarren@wwwdotorg.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>