drm: Keep disabled outputs disabled after suspend / resume

With the current DRM code, an output that has been powered off
from userspace will automatically power back on when resuming
from suspend. This patch fixes this behaviour.

Tested only with the Intel i915 driver on an Intel GM45 Express
chipset.

Signed-off-by: David John <davidjon@xenontk.org>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>