Add MPSSE mode (FT232H emulation)

[gregdavill]

This PR is an initial proof of concept to have the CH32V307 microcontroller act and respond like an FT2232H, so that existing icebreaker examples work without change.

The steps taken are:

• Configure descriptors to mach the original iceBreaker, PID/VID/bcdDevice, and 2 Vendor defined endpoints.
• Implement control endpoint handler to respond like an FT232H device. (Wireshark, libftdi1, and https://krinkinmu.github.io/2020/09/05/ftdi-protocol.html describe the protocol)
• Implement a bulk endpoint handler to parse/match incoming stream of data, MPSSE protocol. (Documented here: https://www.ftdichip.com/Support/Documents/AppNotes/AN_108_Command_Processor_for_MPSSE_and_MCU_Host_Bus_Emulation_Modes.pdf)

Currently only enough functions are implemented to support iceprog -S

[gregdavill]

Another reference, Colin O'Flynn mentioned they've done a similar thing with Chip Whisperer, they handle enough command to support JTAG/SWD. https://github.com/newaetech/naeusb/blob/main/naeusb_mpsse.c