compat: backport memweight()

compat: backport memweight()

mcgrof@frijol ~/linux-next (git::master)$ git describe --contains 639b9e34
v3.6-rc1~41^2~73

commit 639b9e34f15e4b2c30068a4e4485586af0cdf709
Author: Akinobu Mita <akinobu.mita@gmail.com>
Date:   Mon Jul 30 14:40:55 2012 -0700

    string: introduce memweight()

    memweight() is the function that counts the total number of bits set in
    memory area.  Unlike bitmap_weight(), memweight() takes pointer and size
    in bytes to specify a memory area which does not need to be aligned to
    long-word boundary.

    [akpm@linux-foundation.org: rename `w' to `ret']
    Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
    Cc: Anders Larsen <al@alarsen.net>
    Cc: Alasdair Kergon <agk@redhat.com>
    Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
    Cc: Mark Fasheh <mfasheh@suse.com>
    Cc: Joel Becker <jlbec@evilplan.org>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Andreas Dilger <adilger.kernel@dilger.ca>
    Cc: "Theodore Ts'o" <tytso@mit.edu>
    Cc: Matthew Wilcox <matthew@wil.cx>
    Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
    Cc: Tony Luck <tony.luck@gmail.com>
    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>