✨ Add ext reg ena to new TH 64 divsqrt unit
requested to merge github/fork/michael-platzer/feature/new_multifmt_divsqrt_ext_reg_enable into develop
This PR adds the external register enable signal to the wrapper of the new TH64 div/sqrt unit, in the same fashion as it has been added to the other opgroups in #89. As with these earlier changes, if the new reg_ena_i port is tied to '0, then the logic remains semantically equivalent.