pc-dimm: factor out address search into MemoryDevice code

pc-dimm: factor out address search into MemoryDevice code

This mainly moves code, but does a handfull of optimizations:
- We pass the machine instead of the address space properties
- We check the hinted address directly and handle fragmented memory
  better
- We make the search independent of pc-dimm

Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180423165126.15441-6-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>