Place the dtbs-* files in /boot so that upgrades are survivable on RPi
This should relocate the dtbs-* files from /boot/dtbs-rpi,dtbs-rpi4 to /boot, and /boot/dtbs-*/overlays to /boot/overlays. This will make RPi kernel upgrades survivable.
Needs to be tested in CI to validate the files land where desired. May also be desirable to also merge rpi+rpi4 into a single.