hw/s390x/ipl: enable LOADPARM in IPIB for a boot device

hw/s390x/ipl: enable LOADPARM in IPIB for a boot device

Insert the LOADPARM value to the IPL Information Parameter Block.

An IPL Information Parameter Block is created when "bootindex" is
specified for a device. If a user specifies "loadparm=", then we
store the loadparm value in the created IPIB for that boot device.

Initial patch from Eugene (jno) Dvurechenski.

Signed-off-by: Eugene (jno) Dvurechenski <jno@linux.vnet.ibm.com>
Signed-off-by: Farhan Ali <alifm@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>