freedreno: Add a NIR pass to lower backend IO offset computations
This is a subset of the series that was recently sent to mesa-dev for review. It includes only the part that lowers SSBO offsets (roughly last 3 patches of the original series). The rest of the patches for image store/atomic still need more work to address all the issues raised during review, as well as a non-trivial rebase over current master.
The plan is to send the rest of the patches for image (and UBO) as a follow-up.