drm/i915: add SNB and IVB video sprite support v6

The video sprites support various video surface formats natively and can
handle scaling as well.  So add support for them using the new DRM core
sprite support functions.

v2: use drm specific fourcc header and defines
v3: address Daniel's comments:
  - don't take struct mutex around register access (only needed for
    regs in the GT power well)
  - don't hold struct mutex across vblank waits
  - fix up update_plane API (pass obj instead of GTT offset)
  - add interlaced defines for sprite regs
  - drop unnecessary 'reg' variables
  - comment double buffered reg flushing
  Also fix w/h confusion when writing the scaling reg.
v4: more fixes, address more comments from Daniel, and include Hai's fix
  - prevent divide by zero in scaling calculation (Hai Lan)
  - update to Ville's new DRM_FORMAT_* types
  - fix sprite watermark handling (calc based on CRTC size, separate
    from normal display wm)
  - remove private refcounts now that the fb cleanups handles things
v5: add linear surface support
v6: remove color key clearing & setting from update_plane

For this version, I tested DPMS since it came up in the last review;
DPMS off/on works ok when a video player is working under X, but for
power saving we'll probably want to do something smarter.  I'll leave
that for a separate patch on top.  Likewise with the refcounting/fb
layer handling, which are really separate cleanups.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>