drm/i915: Don't complain about stolen conflicts on gen3

Apparently stuff works that way on those machines.

I agree with Chris' concern that this is a bit risky but imo worth a
shot in -next just for fun. Afaics all these machines have the pci
resources allocated like that by the BIOS, so I suspect that it's all
ok.

This regression goes back to

commit eaba1b8f
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu Jul 4 12:28:35 2013 +0100

    drm/i915: Verify that our stolen memory doesn't conflict

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76983
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71031


Tested-by: lu hua <huax.lu@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Paul Menzel <paulepanter@users.sourceforge.net>
Cc: stable@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>