FIX: setting hmap_is_compressed flag correctly

This MR fixes correctly setting the hmap_is_compressed flag in the global and local threshold tuning routines.

Currently, if no scan was conducted before running a tuning e.g. meta_tune_threshold.py, the respective register holds an incorrect value which corrupts the analysis following the tuning and no correct tuning can be found. This just reads the value from the configuration which is also error prone if the chip instance is changed by someone other than the scan itself...