drm/i915: restore RSTDBYCTL only on non-KMS paths

Since RSTDBYCTL is only saved on non-KMS path in within i915_save_state,
move the restore in i915_restore_state for symmetry.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>