s390/cio: rework channel-utilization-block handling

Convert channel-utilization-block (CUB) address variables from separate
named fields to arrays of addresses. Also simplify error handling and
introduce named constants. This is done in preparation of introducing
additional CUBs.

Note: With this change the __packed annotation of secm_area is required
to prevent an alignment hole that would otherwise occur due to the
switch from u32 to dma64_t.

Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>