[enhancement] Provide board definition and blinky example for Red Pitaya

[sanojb]

I would like to try getting rhea to work (board definition and blinky) with the Red Pitaya board (http://redpitaya.com/). I will try an implementation myself, but I would appreciate some feedback if others have already made some experience with it. So let me know if you have tried something!

[cfelton]

@sanojb sorry for the late reply, I have been busy. If you want to give it a go, create a PR with the board definition and I can review it. Otherwise I will get to it when I have time.