drm/i915: remove restore in resume

Don't need extra config restore like for intel_agp, which
might cause resume hang issue found by Alan on 845G.

Cc: Stable Team <stable@kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>