Add loong64 to the list of architectures prepared by prepare_host_binfmt_qemu_cross().
This allows automatic registration and use of qemu-user emulation for LoongArch64
guests, enabling rootfs bootstrap and CI workflows targeting loong64.
This aligns Armbian with Debian’s upcoming native loong64 support (Forky) and allows
testing already via debian-ports and qemu-system-loongarch64.
Signed-off-by: Igor Pecovnik <igor@armbian.com>