drm/i915: Always force a modeset in intel_crtc_restore_mode, v2.

And get rid of things that are no longer true. This function is only
used for forcing a modeset when encoder properties are changed.

Because this is not yet done atomically, assume a full modeset is
needed and force a modeset on the crtc.

Changes since v1:
- s/reset/force modeset/

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>