turnip: initial storage image support (IBO path)
Carving off a part of my work on storage images that I think is ready: Plug in the storage image descriptors in the IBO descriptor slots. This gets
dEQP-VK.image.atomic_operations.* working (IBO access), but not the cmdbuf tests (which just do loads, so sampler-based access).
This MR is effectively only the last 4 commits here, the rest is from !3240 (merged).