Use Raspberry Pi as "Upgrade KIT"

[borzel]

Did some quick testing with an Raspberry Pi 3B and a X32 Core:

Connected Interfaces:

• Power: +5V / GND
• UART to Surface (Buttons / Encoders / LCD)
• SPI to FPGA

It loaded the FPGA Bitstream and I could send audio from Talkback Input to the Headphones :-)
Buttons and the tiny display also worked.