s390/iucv: Provide iucv_alloc_device() / iucv_release_device()

Provide iucv_alloc_device() and iucv_release_device() helper functions,
which can be used to deduplicate more or less identical IUCV device
allocation and release code in four different drivers.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alexandra Winter <wintera@linux.ibm.com>
Link: https://lore.kernel.org/r/20240506194454.1160315-2-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>