Newer Pi4s ship with the so-called C0 processor which can run at 1.8 GHz max
freq gracefully. Add 'arm_boost=1' to pi4 section of config.txt to enable.
This has no effect on older chips (they continue with their 1.50 GHz max unless
users overclock them).
Move dtbs out of /boot/broadcom/ to /boot/ for aarch64 to allow auto detection
on boot rather than hard-coding into /boot/config.txt. Increase flexibility
and matches what RPiOS does with their arm64 image currently.
