drm/i915: disallow clip rects on gen5+

drm/i915: disallow clip rects on gen5+

Unfortunately there has been dri1 userspace that used gem to manage
the gtt and hence also needed cliprects in the execbuf ioctl. So
we can't ever remove that code without breaking the ioctl abi.

But at least we can disable it on gen5+, because these horrible
versions of mesa have not supported these chips.

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