drm: Provide compat ioctl for addfb2.1

Frame buffer modifiers extensions provided in;

  commit e3eb3250
  Author: Rob Clark <robdclark@gmail.com>
  Date:   Thu Feb 5 14:41:52 2015 +0000

      drm: add support for tiled/compressed/etc modifier in addfb2

Missed the structure packing/alignment problem where 64-bit
members were added after the odd number of 32-bit ones. This
makes the compiler produce structures of different sizes under
32- and 64-bit x86 targets and makes the ioctl need explicit
compat handling.

v2: Removed the typedef. (Daniel Vetter)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: Rob Clark <robdclark@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: stable@vger.kernel.org
[danvet: Squash in compile fix from Mika.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>