radv: emit geometry ring size and pointers via preamble (v2)

radv: emit geometry ring size and pointers via preamble (v2)

This uses the scratch infrastructure to handle the esgs
and gsvs rings.

(this replaces the old code that did this with patching).

v2: fix correct ring sizes, reset sizes (Bas)

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