We currently need this either to allocate the next ram_addr_t for a
new block, or for total memory to be migrated.  Both of which we can
calculate without need of this to keep us in a contiguous address space.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>