The source devicetree package can have overlays (dtbo) files. When
applying overlays specified with hardware.deviceTree.overlays, the dtbos
from the source are dropped. Make applyOverlays copy through all non-DTB
files. This matches the behavior when there are no
hardware.deviceTree.overlays described for the system.
In some cases vendor provided .dts's do not have a `compatible` string set
[example](https://github.com/raspberrypi/linux/blob/rpi-6.1.y/arch/arm/boot/dts/overlays/hat_map.dts).
Trying to patch them with `apply_overlays.py` results in an exception (and
therefore build error) even when the filter didn't match this .dtb.
These changes allow patching .dtbs with no `compatible` set, assuming they
are compatible with the overlay.