drm/i915: move dri1 irq ioctl code to i915_dma.c

Let's just get this out of the way.

v2: Rebase against ENODEV changes.

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>