i965/blorp: Don't resolve HiZ unless we're reinterpreting

This MR modifies blorp so that it can safely blit from HiZ at least for blorp_blit with no reinterpreting. This lets us avoid some HiZ resovles for image blits. Unfortunately, it doesn't yet work for blorp_copy so we can't really enable the optimization for ANV yet. Also, I couldn't figure out why this isn't broken for iris today so maybe something needs to be don there?