panfrost: Add PAN_MESA_DEBUG=gl3 flag

This flag allows forcing GL 3.3 without having to use
MESA_GL_VERSION_OVERRIDE etc.

Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5584>
2 files changed