iris: Enable compression for image load/store in more cases
We were calling iris_resource_texture_aux_usage here, which disables auxiliary support if color happens to already be resolved. This makes sense for read only images, where if we know ahead of time that aux doesn't contain any useful information, we can just tell the hardware to not bother looking at it. However, it makes no sense for mutable images, as even if the aux currently has no useful data, we want to produce that data when doing our image writes. Import the bits of logic we need from there and shed the rest. We don't need to consider HiZ, MCS, or MC, nor do we need to do format-based CCS compatibility checks on Gfx12+, so it's actually very little code.