Now that the calculation of the initial memory is hidden in the sclp
device, we can unify the allocation of the initial memory.

The remaining ugly part is the reserved memory for the virtio queues,
but that can be cleaned up later.
Reviewed-by: NMatthew Rosato <mjrosato@linux.vnet.ibm.com>
Signed-off-by: NDavid Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>