Use systemd init instead of busybox init for mkinitcpio

### describe the request

Busybox init has limitations compared to systemd init, the most major is that you can't auto-unlock LVM2 root volume with TPM2 PCR11 since busybox init doesn't write UKI hash to PCR. 
https://wiki.archlinux.org/title/Mkinitcpio#Common_hooks