drm/i915: quirk away broken OpRegion VBT

Somehow the BIOS manages to screw things up when copying the VBT
around, because the one we scrap from the VBIOS rom actually works.

Cc: stable@kernel.org
Tested-by: Markus Heinz <markus.heinz@uni-dortmund.de>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=28812
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>