drm/i915: Use drm_plane_state.{src,dst,visible}

Replace the private drm_rects/flags in intel_plane_state
with the ones now living in drm_plane_state.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1469549224-1860-5-git-send-email-ville.syrjala@linux.intel.com