Adapt the environment and test-bench to execute the AXI agent in active/passive mode

Created by: AEzzejjari

This commit allows to us switch the axi_agent mode without changing any part of code. There is two way to change the agent mode:

First way: From env_cfg we can change the variable axi_cfg.is_active to UVM_PASSIVE or UVM_ACTIVE. Second: From command line by using --axi_active option.