Fastboot is part of Android's AOSP distribution and can't easily be built seperately unfortunately and many vendors that also use fastboot (such as Sipeed on their Lichepi4A SBC), distribute binaries for x86 only. That is a real shame, however...
When needed on any ArchPOWER supported platform, you can emulate it using qemu.
pacman -Sy qemu-user-static x86_64-pc-linux-gnu-gcc
sudo qemu-x86_64-static -L /usr/x86_64-pc-linux-gnu ./fastboot
This has been tested with Sipeed's burn_tools (taken from burn_tools_support_bigimage.zip) and works albeit naturally slowly on startup especially when flashing large images.