[RFC][PATCH] Atomic page flip WIP

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