Sysutils/u-boot-rpi3 differs from normal ports. Make install deposits
u-boot.bin in /usr/local/share/u-boot/u-boot-rpi3, from which it
must be copied to /boot/msdos/u-boot.bin.

Meanwhile, /boot/loader.efi is updated by buildworld, but must be
copied to /boot/msdos/EFI/BOOT/bootaa64.efi so that u-boot.bin
can find and execute it.