shmem: Turn shmem-info into shared objects from shremap ones

We have a nasty issue with it. Current code allocates these
entries in shremap area one by one. We do NOT allocate any
OTHER entries in this region, but if we will this array will
be spoiled.

Fortunately we no longer need shmem-infos as plain array,
neither we need one in restorer. So just turn this into plain
shared objects and collect them in a list.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>