panfrost: Cleanup point sprite linking

Use the common Gallium helper, and get the sprite coord mask from the
rasterizer instead of the shader state (which requires useless keying).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6476>
1 file changed