Create a lot more tests for place and route

[mithro]

Currently the tests are;

• Single FF
• Single LUT
• PicoRV32

That is a pretty big jump from the simple cases to the full CPU.

Would be good to add some simple tests like;

• Large multiplexer
• Shift register
• Simple echo UART type device

Then after the picorv32, we should go onto a full SoC with DDR controller and internal peripherals on a wishbone bus.

[mithro]

Would also be a good idea to test different flip flop types.

Some type of clock-domain-crossing would be good.