[RFC] Updated plane support v3

[Jesse Barnes]

This version adds both source and dest rect params to the set_plane
ioctl, and makes the source fixed point to support hardware that needs
it.

I haven't changed the name of the SNB implementation yet (per Chris's
suggestions) but will before it gets upstream.

I'd be interested to see whether these interfaces will work for other
hardware, so please take a close look at them and ideally implement them
on your hardware to make sure (see my userspace example code from
earlier posts if you want something to crib from).

Thanks,
Jesse