mkinitfs: also match *.ko.zst initfs modules

The new lts kernel uses zstd to compress modules, which makes the files end with .ko.zst instead of *.ko. As such mkinitfs will fail to include those modules in the initramfs.

I don't know which is the best approach here. Adding * seems vague. Maybe we can do find -name "*.ko" -or -name "*.ko.zst"? Leaving the MR here for some guidance.