qemu-base installs all the x86 stuff, which you probably don't need or want. I installed just qemu-system-aarch64 and I'm emulating aarch64 machines. This may work with qemu-system-arm too, but I haven't tried it, YMMV.
qemu-system-aarch64 depends on edk2-armvirt. This has been replaced with the split edk2-arm and edk2-aarch64 packages, so you'll have to manually download and install edk2-armvirt from
https://archive.archlinux.org/packages/e/edk2-armvirt/. Fortunately these are all noarch packages so pulling them from the x86 repos is an option.
I'm using edk2-armvirt-202111-1-any.pkg.tar.zst and it works fine.
As for the libbpf dependency, I'm not sure. I have libbpf 0.8.1-1 installed, from the libbpf package. Try just "pacman -S libbpf" and it might get you there.
So to run aarch64 VMs: install libbpf, download and install (with pacman -U) edk2-armvirt, and then install qemu-system-aarch64.
Let me know if you absolutely must install qemu-base, there's a way to do that too.
EDIT: I see the latest version of core/libbpf is 1.0.1-1. This might be too new for the 7.0 version of qemu. Maybe you can find an older version if so. Good luck.
EDIT EDIT:
DON'T use a newer version of the OVMF files from a newer edk2 package. It won't work. For example, you can install the edk2-aarch64 package, but if you use the UEFI files it provides, qemu won't boot. Use an older edk2-armvirt package as indicated above.