The recent rpi-firmware update renamed "0" to "zero" in the RPi0 DTB
filename
It also included the components needed to boot the RPi4, so install those
now -- interested parties can install sysutils/u-boot-rpi4 and copy
config_rpi4.txt to config.txt on the FAT partition in order to boot the
board. Do note that we currently don't support ethernet/usb/pci.
Reviewed by: manu
MFC after: 3 days
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