s390-bios: Factor finding boot device out of virtio code path

Make a new routine find_boot_device to locate the boot device for all
cases, not just virtio.

The error message for the case where no boot device has been specified
and a suitable boot device cannot be auto detected was specific to
virtio devices. We update this message to remove virtio specific wording.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <1554388475-18329-12-git-send-email-jjherne@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
2 files changed