Create FTDI emulation firmware

[mithro]

• https://github.com/mithro/fx2-ftdi-emulation
• https://docs.google.com/document/d/1o4jDru_V9IBvkkuhyQb1zBzm_QvzDBo2B5adP2bvahY/edit
• https://docs.google.com/document/d/1xGOBDtByU6D7ry2WnLUE_slqmjgId_JAscZK3gMCLug/edit