If concurrent PMD population has happened, re-use orphaned memblocks.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b29ffffb9206dc14541fa420c17604240728041b.1579024426.git.christophe.leroy@c-s.fr