[Intel-gfx] Plane support for SNB and IVB

[Jesse Barnes]

I think the core support is ready now, but I'd like feedback on the
color key ioctl.  It would be good to have a way to disable it at
runtime (w/o color keying enabled, the sprite will always sit on top of
the primary), and potentially add alpha support at some point.

Would 0 as the color key work well enough as a "disable" flag?  Or
should I add a separate field to the ioctl?  Anyone have a preference?

Thanks,
Jesse