Use a prebuilt grub image for EFI, creating BOOT/EFI/grub.cfg

See ALT bug 31971

All drm modules are added to the first and second stages, except
for nouveau and nvidia. Nouveau is added to stage2. nvidia needs
to be added to live and the base system separately. This is an
auxiliary target.

See also https://bugzilla.altlinux.org/31971

See https://bugzilla.altlinux.org/45792

The installer works more reliable when loaded to RAM.