s390/ipl: unite diag308 and scsi boot ipl blocks

Ipl parm blocks received via "diag308 store" and during scsi boot at
IPL_PARMBLOCK_ORIGIN are merged into the "ipl_block".

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>