drm/i915: rip out dri1 breadcrumb updates from gen5+ irq handlers

We never supported dri1 on gen5+.

VLV never had that code, so no need to remove it.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>