s390-bios: decouple common boot logic from virtio

s390-bios: decouple common boot logic from virtio

Create a boot_setup function to handle getting boot information from
the machine/hypervisor. This decouples common boot logic from the
virtio code path and allows us to make use of it for the real dasd boot
scenario.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <1554388475-18329-4-git-send-email-jjherne@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>