mesa: Delay display list save dispatch setup until Exec is set up.

mesa: Delay display list save dispatch setup until Exec is set up.

This will let us copy from the Exec dispatch to deal with our commands that
don't get compiled into display lists.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>