gnu: make-iso9660-image: Do not compress any kernel, compress man pages.
Because the linux image is called differently based on the architectures,
see system-linu/-image-file-name from gnu/system.scm, the kernel image
on aarch64, mips and armhf has still been compressed. This means that
grub cannot boot.
Man pages have moved from gz to zst, so compress them as well.
* gnu/build/image.scm (make-iso9660-image): Do not compress Image, vmlinuz and
zImage; Compress all man pages.
Change-Id: I68b35f383c84ff231865d580aa9e79d9fd88ace1
Signed-off-by: Rutherther <rutherther@ditigal.xyz>