drm: Disable the unused connectors explicitly when resuming with KMS.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>