drm/i915: Make crtc checking use the atomic state, v2.

Instead of allocating pipe_config on the stack use the old
crtc_state, it's only going to freed from this point on.

All crtc' are now only checked once during modeset,
because false positives can happen with encoders after
dpms changes and to limit the amount of errors for 1 failure.

Changes since v1:
- crtc_state -> old_crtc_state
- state -> old_state

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>