[PATCH] drm: drm_rect and clipping for intel sprite planes

[ville.syrjala at linux.intel.com]

I'm re-sending this whole plane clipping series, as it has been a quite
while since the last time I posted it.

Laurent went through patch 1 and I made the requested changes, and I also
fixed a minor issue in patch 3 that I spotted myself.

The other patches are unchanged and looking for volunteers to review them...