The current s390 machine uses the virtio console as default console,
but this doesn't mean that we always want to keep it that way for new
machines.
This patch introduces a way for a machine type to specify that it wants
the default console to be an SCLP console, which is a lot closer to what
real hardware does.
Signed-off-by: Alexander Graf <agraf@suse.de> Reviewed-by: Andreas Färber <afaerber@suse.de>