s390/sclp: clean up, use sccb_mask_t where appropriate

Replace hardcoded instances where 32 or unsigned int (or long) is used
for SCLP event masks, and replace with sizeof(sccb_mask_t) and
sccb_mask_t respectively.

This improves readability and prepares for when we will increase
sccb_mask_t to 64 bits.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>