drm/i915: Make intel_display_suspend atomic, try 2.

Calculate all state using a normal transition, but afterwards fudge
crtc->state->active back to its old value. This should still allow
state restore in setup_hw_state to work properly.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>