pc-bios/s390-ccw: Pass selected SCSI device to IPL

There is ,bootindex=%d argument to specify the lookup order of
boot devices.

If a bootindex assigned to the device, then IPL Parameter Info Block
is created for that device when it is IPLed from.

If it is a mere SCSI device (not FCP), then IPIB is created with a
special SCSI type and its fields are used to store SCSI address of the
device. This new ipl block is private to qemu for now.

If the device to IPL from is specified this way, then SCSI bus lookup
is bypassed and prescribed devices uses the address specified.

Signed-off-by: Eugene (jno) Dvurechenski <jno@linux.vnet.ibm.com>
Signed-off-by: Alexander Yarygin <yarygin@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
