drm/i915: Avoid saving/restore the modesetting registers twice in KMS mode

In KMS mode we now use the normal mode-setting paths to set the modes
back to the current configuration, so we don't need to also run the more
limited non-KMS implementation of modesetting for resume.

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