s390-ccw: interactive boot menu for scsi

s390-ccw: interactive boot menu for scsi

Interactive boot menu for scsi. This follows a similar procedure
as the interactive menu for eckd dasd. An example follows:

    s390x Enumerated Boot Menu.

    3 entries detected. Select from index 0 to 2.

Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
[thuth: Added additional "break;" statement to avoid analyzer warnings]
Signed-off-by: Thomas Huth <thuth@redhat.com>