Call MADV_MERGEABLE on guest memory allocations.  MADV_MERGABLE will be
available starting in Linux 2.6.32.  This system call registers a region of
virtual address space with Linux as a candidate for transparent memory
sharing.

Patchworks-ID: 35447
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>