tmem: save/restore/migrate/livemigrate and shared pool authentication

tmem: save/restore/migrate/livemigrate and shared pool authentication

Attached patch implements save/restore/migration/livemigration
for transcendent memory ("tmem").  Without this patch, domains
using tmem may in some cases lose data when doing save/restore
or migrate/livemigrate.  Also included in this patch is
support for a new (privileged) hypercall for authorizing
domains to share pools; this provides the foundation to
accomodate upstream linux requests for security for shared
pools.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>