Debian 12's initrd by default now consists of an uncompressed cpio
archive containing microcode, followed by a zstd-compressed cpio
archive. inject_firmware.sh only supported gzip-compressed cpio, so it
could not extract /init from this archive.
Add zstd-decompress to decompress zstd streams (uncompressed size is
about 180 KB).
Add unpack_initramfs.sh which is able to decompress uncompressed, gzip,
or zstd archives, with multiple segments, much like the Linux kernel
itself does.
Use unpack_initramfs.sh to extract /init for blob jail.
Don't compress the new archive segment containing firmware and the
updated /init.
Signed-off-by: Jonathon Hall <jonathon.hall@puri.sm>
