Add arm64 uefi support, bump systemd third_party

This PR:

adds the systemd-bootaa64.efi file to support UEFI boot for arm64/aarch64 machines that can do UEFI.
bumps the systemd package from systemd-248.3-2 to systemd-250.5-1 (I couldn't find the arm64 version for systemd-248.3-2 in any archive, so I bumped them both).

The packages come from the arch linux package registries:

amd64: https://archlinuxarm.org/packages/aarch64/systemd
arm64: http://mirror.archlinuxarm.org/aarch64/core/systemd-250.5-1-aarch64.pkg.tar.xz

I successfully tested this with a qemu arm64 machine with the following config :

# note: I had to build the drive.img with -serial_console="ttyAMA0,115200"
qemu-system-aarch64 \
  -name gokrazy-arm64 \
  -m 3G \
  -smp $(nproc) \
  -M virt,highmem=off \
  -cpu cortex-a72 \
  -nographic \
  -netdev user,id=net0,hostfwd=tcp::8080-:80,hostfwd=tcp::2222-:22 \
  -device e1000,netdev=net0 \
  -drive file=drive.img,format=raw \
  -bios /usr/share/qemu-efi-aarch64/QEMU_EFI.fd

This is partly related to the discussion at: https://github.com/gokrazy/gokrazy/issues/129

gokrazy / tools

Add arm64 uefi support, bump systemd third_party #36