pan/bi: Collect return addresses of blend calls

We will need that for blend shaders so they can be passed a return
address and jump back to the fragment shader when they're done.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7151>
4 files changed