The fallback loader, /boot/efi/EFI/BOOT/bootaa64.efi or bootx64.efi,
cannot be upgraded by shim-install on SL Micro. The issue case is
SL Micro 6.0. It causes that system gets regression bug because it's
fallback to a old shim. So this patch adds ca_string to SL Micro.
(bsc#1254336)