grub.macros: Install font in /boot/grub2 instead of the ESP
    
    GRUB is now using /boot/grub2 as the directory where all the resources are
    loaded, but the unicode.pf2 is still installed in the EFI System Partition.
    
    Resolves: rhbz#1739762
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>