- Bump version: 9.25.11 → 9.25.12

- Fix double grub entries in hybrid ISO images
As consequence of using the "source" grub command instead
of the "configfile" command to load the grub config we now
see double loading of the same file on ISO media. The reason
here is that kiwi ISO media is always hybrid which means it
embeds an MBR into the ISO for which the "source" command now
can read the same file through two different device paths.
This does not happen with the "configfile" grub command.
Thus this patch uses "configfile" if we produce an ISO image
and "source" for all other image types. The commit also fixes
the custom grub template used for ISO images in a way that
we only set the "serial" command if there is a serial
configuration provided along with the image description.

- Update x86/tumbleweed/test-image-systemd-boot
systemd package has been splitted and provides
systemd-boot in an extra package now

- Limit scope of grub _fix method
Only apply _fix_grub_to_support_dynamic_efi_and_bios_boot for
the x86_64 or ix86 architectures. This Fixes #2343