[RFC][PATCH] Atomic page flip WIP

[ville.syrjala at linux.intel.com]

I'm posting this as rather raw just to get a bit more substance to the
discussions.

The drm_flip thingy may seem a bit too mid-layerish for people's taste,
but at least it is almost completely driven by explicit function calls
from the driver (the wq side is the exception naturally).

I originally wrote drm_flip for Medfield, where I used it syncronize the
pipe's primary layer and one or two video overlays (gen3 style overlays).
So it's a fairly well proven tehnology. I can post a version of the video
overlay code too in case someone would be interested in having drm_planes
on gen3 hardware.

This set applies on top of my earlier drm_atomic_4 branch:
https://gitorious.org/vsyrjala/linux/commits/drm_atomic_4