softpipe: don't abuse the draw vertex_info struct for something different

softpipe: don't abuse the draw vertex_info struct for something different

softpipe would calculate two "vertex layouts". The second one was however
just used for internal purposes, draw would know nothing about it even though
it looked exactly the same as the other one we tell draw about.
So, store that information separately as this was just confusing.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>