drm/i915: rip out intel_dpio_write again

Unfortunately it looks like further vlv patches are still stalled due
to fried hw, and too many people are a bit annoyed about the unused
function warning.

So let's just rip it out, we can easily put it back in again.

Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>