lib/bitmap.c: conversion routines to/from u32 array

lib/bitmap.c: conversion routines to/from u32 array

BugLink: http://bugs.launchpad.net/bugs/1635721
Aimed at transferring bitmaps to/from user-space in a 32/64-bit agnostic
way.

Tested:
  unit tests (next patch) on qemu i386, x86_64, ppc, ppc64 BE and LE,
  ARM.

Signed-off-by: David Decotigny <decot@googlers.com>
Reviewed-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit e52bc7c28ac9f54db6f86b19ed65c599def18c98)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>