Improve support for RPi1 revisions

[picosonic]

RPi1 B - 26-pin GPIO header had some pinout changes between revision 1 and 2.

Currently all detected RPi1 revision codes are treated the same.

However the 26 pins of the B board revision 2 match the 40 pin GPIO pinouts of later models.

Pin 3 was GPIO0 on Rev 1 and GPIO2 on Rev 2
PIn 13 was GPIO21 on Rev 1 and GPIO27 on Rev 2

https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#raspberry-pi-revision-codes

This means revision codes found in /proc/cpuinfo of 0002 and 0003 might need to be treated differently to all other RPi1 pinouts.

This does need testing on actual hardware.