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>