radv: reduce CPU overhead merging bo lists.

radv: reduce CPU overhead merging bo lists.

Just noticed we do a fair bit of unneeded searching here.

Since we know that the buffers in a CS are unique already,
the first time we get any buffers, we can just memcpy those into
place, and when we are searching for subsequent CSes, we only
have to search up until where the previous unique buffers were.

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