introduce memory_region_get_alignment() that returns
underlying memory block alignment or 0 if it's not
relevant/implemented for backend.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>