drm/i915: Restore skl_gt3 device info

This was broken in

commit 6a8beeff
Author: Wayne Boyer <wayne.boyer@intel.com>
Date:   Wed Dec 2 13:28:14 2015 -0800

    drm/i915: Clean up device info structure definitions

and I didn't spot this while reviewing. We really need that CI farm up
asap!

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Wayne Boyer <wayne.boyer@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>