pc-bios/s390x: Enable multi-device boot loop

pc-bios/s390x: Enable multi-device boot loop

Allow attempts to boot from multiple IPL devices. If the first device fails to
IPL, select the pre-built IPLB for the next device in the boot order and attempt
to IPL from it. Continue this process until IPL is successful or there are no
devices left to try.

Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20241020012953.1380075-18-jrossi@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>