osdep/linux/getroot: Detect DDF container similar to IMSM

osdep/linux/getroot: Detect DDF container similar to IMSM

Similarly to Intel IMSM, there are BIOS and UEFI implementations that
support DDF containers natively.

DDF and IMSM are very similar in handling, especially these should not
be considered as RAID abstraction. This fixes the requirement of having
a device map when probing DDF containers.

Fixes: https://issues.redhat.com/browse/RHEL-44336
Signed-off-by: Renaud Métrich <rmetrich@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>