You copied the wrong efi file. You should copy /boot/boot1.efi to bootaa64.efi. boot1.efi then loads loader.efi, and it tells loader.efi which partition it's loaded from, so loader.efi can then load the kernel.
Here are some easier directions to get started:
0. Build and flash the uboot firmware with EFI support using the git tree I posted.
1. Download the RPI aarch64 image. This image already has the EFI directory structure in place, as well as DTB in the fat boot partition.
2. Configure uboot:
setenv bootcmd 'load mmc 0:1 $fdt_addr dtb/marvell/armada-3720-espressobin.dtb; load mmc 0:1 $kernel_addr EFI/BOOT/bootaa64.efi; bootefi $kernel_addr $fdt_addr'
3. You should be able to boot into FreeBSD 13. The EFI loader loads the device tree and passes to the kernel.