drm/i915: Make updating pipe without modeset atomic.

Instead of doing a hack during primary plane commit the state
is updated during atomic evasion. It handles differences in
pipe size and the panel fitter.

This is continuing on top of Daniel's work to make faster
modesets atomic, and not yet enabled by default.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet:
- simplify/future-proof if ladder that Jesse spotted
- resolve conflict in pipe_config_check and don't spuriously move the
  code.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>