turnip: Treating non-d/s-write pipelines as not having d/s feedback loops.

turnip: Treating non-d/s-write pipelines as not having d/s feedback loops.

A subpass in gfxbench has the depth buffer present, but not written to,
for a render pass using the depth buffer as an input attachment.  We can
skip single-prim-mode and the associated "oh no don't use sysmem" in that
case.

Improves gfxbench vk-5-normal perf by 1.56193% +/- 0.0743035% (n=14).
Part of #6327.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18241>