anv: Avoid sampling some MCS surfaces with clear
Supposedly avoids GPU hangs in BF4. See HSD 1707282275 and 14013111325. v2. Fix bug in WA implementation. (Sagar) Cc: mesa-stable Reviewed-by:Sagar Ghuge <sagar.ghuge@intel.com> Part-of: <mesa/mesa!8755> (cherry picked from commit eef4c708)