Support multiple clocks for Verilator Simulation

[P-Miranda]

Verilator simulation toggles clocks from function Timer() in iob_tasks.cpp and only supports a single hardcoded clk.

• Update iob_tasks.cpp to support multiple clocks
• or add pointer to custom Timer() function that can be implemented in iob_soc_tb.cpp or equivalent top level testbench for verilator.

This applies to all branches and relates to .cpp files that are not directly affected by if_gen2 developments.

[jjts]

We have tried this before; isn't there a timing directive that causes issues?