freedreno/a6xx: Move layer_zero handling to interp state

We can just bake this into the program state, rather than making it a
shader variant.  Turnip had already switched to this approach so it will
let us drop ir3 lowering for this.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19236>
2 files changed