This code currently relies on mem_hotplug_begin()/mem_hotplug_done() -
create_section_mapping()/remove_section_mapping() implementations
cannot tollerate getting called concurrently.

Let's prepare for callers (memtrace) not holding any such locks (and
don't force them to mess with memory hotplug locks).

Other parts in these functions don't seem to rely on external locking.
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201111145322.15793-5-david@redhat.com