Added partial Raspberry Pi 4 support

[1anakin20]

I have achieved to make this work partially on the Pi 4. By guessing my way with the datasheet and by copy pasting from this PiFmRDS updated file who aims to support the Pi 4, and lots of luck. Mainly, it was updating the addresses. I have no clue how I made it work.

However, as I said, it is partial. With the RC car I tested it with, I could only achieve it to go forwards. I am unsure it is the RC car I tested it with or something else. I don't believe much it is the car. The RC car works fine with the Pi 2. I don't know enough about low level to figure it out.

The code is in my fork pi4 branch: https://github.com/1anakin20/pi-rc/tree/pi4