rpm2cpio.sh: update to the last 4.x version

openSUSE RPMs are compressing the RPM payload using zstd, that
correspond to the magic ID 0x28, 0xb5, 0x2f.

This patch update the script to the last version from the rpm project,
and add support to this compression format, and extract the cpio payload
using the "unzstd" binary.

Signed-off-by: Alberto Planas <aplanas@suse.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>