grub.macros: Use consistent file mode for legacy and EFI
    
    Currently the permissions are inconsistent for grub2-pc and grub2-efi:
    
    $ rpm -qlvf --filesbypkg /boot/grub2/grub.cfg
    ...
    grub2-efi-x64             /boot/grub2/grub.cfg
    -rwx------    1 root     root
    grub2-pc                  /boot/grub2/grub.cfg
    -rw-r--r--    1 root     root
    
    Resolves: rhbz#1965794
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>