[arm-allstar] Pi 4/Pi 3 B+ thermal review with firmware improvements

[Jason]

Interesting bit is board orientation that can reduce temperature by 2C and
slow warm up under load. With the firmware improvements and orientation you
could probably get by fine with just heat sinks with the Pi 4 now. My Pi
3B+ ASL/DVSwitch node does fine with just heat sinks (building that node
gave me a much greater appreciation for Hamvoip's version, improvements,
documentation).

https://www.raspberrypi.org/blog/thermal-testing-raspberry-pi-4/

73
Jason - N6WBL