drm/i915: disable LVDS clock gating on CPT v2

Needed to prevent display corruption in high res panels.

v2: use correct unit names (Rodrigo)

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Ulrich Drepper <drepper@gmail.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>