drm/i915/kbl: drm/i915: Avoid GuC loading for now on Kabylake.

GuC has no version for KBL published yet and it is not recommended
to load the Skylake one, so let's avoid loading this for now while
we don't have the proper GuC firmware for Kabylake.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Alex Dai <yu.dai@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449622718-21684-1-git-send-email-rodrigo.vivi@intel.com