Add Upduino board support

[m00dawg]

This is my first pass and to be clear I'm not sure I know what I'm doing :P But I got an Upduino to do FPGA things, among them is to play with a FemtoRV core. Upduino seems similar to Icebreaker based on some threads in Discussions so thought I'd take a crack at seeing if I can at least make things compile. Still waiting for the hardware arrive to properly test.

[Jonaswinz]

To successfully compile for the Upduino, the linker script for the board is missing (in FemtoRV/FIRMWARE/CRT). I just duplicated the spiflash_icebreaker.ld and renamed it to spiflash_upduino.ld, because the chip (ICE40UP5K) and flash size (4MB) are the same, at least for my Upduino 2.1. I also successfully flashed the code to the FPGA, but I was not able to get a USB serial connection. I think this is due to the hardware design of the Upduino: The pins of the ICE40 chip, which are connected to the FT323 TX and RX lines, are shared with the flash. @m00dawg did you managed to get everything running ?