Unify GRUB configuration file location across all platforms
    
    The GRUB configuration files layout on EFI platforms isn't consistent with
    other non-EFI platforms (e.g: legacy BIOS x86 and Open Firmware ppc64le).
    
    On platforms using EFI, the GRUB config file (grub.cfg) and environment
    variables block (grubenv) are stored in the EFI System Partition (ESP),
    while for non-EFI platforms these are stored in the boot partition (or
    /boot directory if not boot partition is used).
    
    The reason for this is that the path where the GRUB bootloader searches
    for its configuration file varies depending on the firmware interface.
    
    For EFI the GRUB binary is located in the ESP and it expects to find its
    config file in that location as well. But this creates the mentioned
    inconsistency, because the GRUB configuration file has to be stored in
    /boot/efi/EFI/fedora/grub.cfg while for non-EFI platforms it has to be
    stored in /boot/grub2/grub.cfg.
    
    To allow all platforms to have the GRUB config file in the same location,
    only a minimal config file could be stored in the ESP and this will load
    the one that is stored in /boot/grub2.
    
    Related: rhbz#1918817
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>