nir: Add a face_sysval argument to nir_lower_two_sided_color

This is needed for handling drivers that use an input for loading the
face, for example Panfrost with Midgard GPUs.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Tested-by: Urja Rannikko <urjaman@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5915>
6 files changed