vulkan,lavapipe: Simplify command recording code-gen

vulkan,lavapipe: Simplify command recording code-gen

The Entrypoint class already has utilities for gettingt he parameter
list as either declarations or as comma-separated argument names for a
call.  Use that instead of hand-rolling it.  The only modification we
need to make is to add the ability to start the list somewhere other
than at the beginning.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14919>