Add loongarch64 support

[am11]

Closes #19

I was testing it with podman desktop on macOS, as docker desktop does not has binfmt registration docker/roadmap#764.

% podman run --rm --privileged --pid=host debian nsenter -t 1 -m -u -n -i cat /proc/sys/fs/binfmt_misc/qemu-loongarch64
enabled
interpreter /usr/bin/qemu-loongarch64-static
flags: OCF
offset 0
magic 7f454c4602010100000000000000000002000201
mask fffffffffffffffc00fffffffffffffffeffffff

% echo "7f454c4602010100000000000000000002000201" | sed 's/../\\x&/g'
\x7f\x45\x4c\x46\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x02\x01

% echo "fffffffffffffffc00fffffffffffffffeffffff" | sed 's/../\\x&/g'
\xff\xff\xff\xff\xff\xff\xff\xfc\x00\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff

First version https://pkgs.alpinelinux.org/packages?branch=v3.21&arch=loongarch64