anv/sparse: misc simple improvements and fixes

There are quite a few Sparse-related series in-flight looking for review (!27306, !28190 and !28347 being the biggest ones). I still have one more change I wanted to do on top of everything but it would generate conflicts with everything, so let me try to get the simplest things merged first (and hope the others also get reviews, at least to their simpler patches) so I can hopefully work in a conflict-free environment.