powerpc: Make the CMM memory hotplug aware

The Collaborative Memory Manager (CMM) module allocates individual pages
over time that are not migratable.  On a long running system this can
severely impact the ability to find enough pages to support a hotplug
memory remove operation.

This patch adds a memory isolation notifier and a memory hotplug notifier.
The memory isolation notifier will return the number of pages found in
the range specified.  This is used to determine if all of the used pages
in a pageblock are owned by the balloon (or other entities in the notifier
chain).  The hotplug notifier will free pages in the range which is to be
removed.  The priority of this hotplug notifier is low so that it will be
called near last, this helps avoids removing loaned pages in operations
that fail due to other handlers.

CMM activity will be halted when hotplug remove operations are active and
resume activity after a delay period to allow the hypervisor time to
adjust.

Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Brian King <brking@linux.vnet.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Gerald Schaefer <geralds@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>