drm/i915: Kill DRI1 cliprects

Passing cliprects into the kernel for it to re-execute the batch buffer
with different CMD_DRAWRECT died out long ago. As DRI1 support has been
removed from the kernel, we can now simply reject any execbuf trying to
use this "feature".

To keep Daniel happy with the prospect of being able to reuse these
fields in the next decade, continue to ensure that current userspace is
not passing garbage in through the dead fields.

v2: Fix the cliprects_ptr check

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Dave Gordon <david.s.gordon@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>