Enable RVFI Agent monitor's AP by default

This PR solves the issue discussed in MikeOpenHWGroup/cv32e20-dv pull-request #2 in which the AP had to be enabled by manually hacking vendor_lib/openhwgroup_core-v-verif/lib/uvm_agents/uvma_rvfi/uvma_rvfi_cfg.sv. It also attempts to clean up a few minor issues related to the UVM test that runs most simulations in this environment.