drm: replace drawable ioctl by noops

The information supplied by userspace through these ioctls is only
accessible by dev->drw_idr. But there's no in-tree user of that.
Also userspace does not really care about return values of these ioctls,
either. Only hw/xfree86/dri/dri.c from the xserver actually checks the
return from adddraw and keeps on trying to create a kernel drawable
every time somebody creates a dri drawable. But since that's now a noop,
who cares.

Therefore it's safe to replace these three ioctls with noops and rip
out the implementation.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>