99-grub-mkconfig: Also disable BLS usage for Xen Dom0 hosts
A previous patch disabled BLS usage for Xen Dom0 guests but it turns out
that Xen Dom0 hosts also need to regenerate a GRUB config file since the
menuentries used aren't the generated by 10_linux but by 20_linux_xen.
Resolves: rhbz#1761799
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Steven Haigh <netwiz@crc.id.au>