Actually I wasn't going to answer this. But I realized if I won't, no one is going to tell the things I'm going to tell you
. Hear me bro:
1- The PID controller design is a very serious business. There is a whole section of engineering, namely the control engineering, related to it. So I wish it were that easy like plug and control. So you need model of your DC motor, and lots of simulink simulations. Actually there might be some samples from fpga manufacturers, but I don't know.
2- Do not expect to find a magical open code for "Mystical Box for PID Control". Some companies do have generic designs, however they do not share it. If you are able to write one, do share with us
3- One last thing is if you are doing a project on it, it means that you are venturing around the limits of the human knowledge. So you should be expecting undiscovered lands, at least undiscovered for you, expect harsh working conditions, sleepless nights and grinding as used in gaming.
So I believe I didn't answer your question, but hopefully these will help in your engineering carreer. At least I would have wished someone told me these. As a result, do not expect help when asking questions like "how to design best circuit in the world", ask help for the problems in your path. And from your question I can understand that you haven't worked on PID controllers anyway.
Edit: Man this sounded like a motivational speech. Anyway that wasn't my intention. My intention was to tell you why your question won't get an answer.