panfrost: XMLify beginning of shader descriptor

We have just enough abstracted now to pack this ahead-of-time, during
the CSO create, instead of at draw-time. But it's only a start.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6440>
8 files changed