radv: start conditionalising vertex inputs. (v2)

radv: start conditionalising vertex inputs. (v2)

In practice this will probably just drop draw id in a few places.

v2: just do draw_id for now. (Bas)
it might be possible to do something more if we need it in the
future. (nha)

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Dave Airlie <airlied@redhat.com>