Support for rockylinux EFI

@phrancesco

RockyLinux boot failed with latest curtin installer (21.3-14-g9ef03d7f-0ubuntu1~focal). I am getting the below error message:

error: …/…/grub-core/fs/fshelp.c:258:file
‘/boot/vmlinux-4.18.0-305.25.1.el8_4.x86_64’ not found.
error: …/…/grub-core/loader/i386/efi/linux.c:94:you need to load the kernel first.

Press any key to continue…

Failed to boot both default and fallback entries.

Press any key to continue…

Refer: RockyLinux 8.4 booting failed