Adding Raspberry Pi 400

[Chuckduey]

The new Raspberry Pi 400 is a new CPU board built into a keyboard. It still has the same 40 pin connector as the other Pi's but not as easy to put on a hat. A simple cable and it can still run the and see the hats. The Revision code from /prco/cpuinfo is coming up as c03130 - Raspberry Pi 400 Rev 1.0 and is confirmed by the Raspberry Pi Org site https://www.raspberrypi.org/documentation/hardware/raspberrypi/revision-codes/README.md If no one already has one, I can start working on a new PR adding the new Pi platform to the raspberry_pi.c and raspberry pi.h

Best regards

Chuck