migration: Add VMSTATE_UNUSED_VARRAY_UINT32

VMSTATE_UNUSED_VARRAY_UINT32 is used to skip a chunk of the stream
that's an n-element array;  note the array size and the dynamic value
read never get multiplied so there's no overflow risk.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170203160651.19917-2-dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
