s390/sclp: Define commands for storage (un)assignment

Replace immediate values with SCLP_CMDW_UN|ASSIGN_STORAGE defines.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20240610151048.2548428-1-agordeev@linux.ibm.com


Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>