Adding support for the iceFUN board

[ej159]

I'm working to get a servant running on an iceFUN board.

The changes I have made here allow me to run the following command without errors to give code I can upload to my device.

fusesoc run --target=icefun --tool=icestorm servant --pnr=next

I have noticed that icestick and icebreaker also give similar errors relating to PLLs.

It would be nice to expand this so that a simple example (e.g. zephyr_phil) can be run on the board easily in one line as a demo.