pre-dump: don't allow --lazy-pages option

Using --lazy-pages with pre-dump causes partial memory dump and it's not
the intention. The whole point of pre-dump is to keep amount of memory that
would be dumped during tasks freeze to minimum.

Disallow running pre-dump with --lazy-pages.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>