* Overlay surface alpha is configured separately from the overlay. This
prevents display glitches (configure and fill the overlay first, set
alpha to a visible value next)
* Added an ioctl for configuring transparency of the Overlay and graphics
planes. Blend mode, colorkey mode and global alpha mode are supported.
* Added an ioctl for setting the plane order. The overlay plance can be placed
over or
under the graphics plane.
* Added an ioctl for setting and reading chip registers, with mask.