powerpc/pseries: Update the device tree correctly for drconf memory add/remove

This updates the device tree manipulation routines so that memory
add/remove of lmbs represented under the
ibm,dynamic-reconfiguration-memory node of the device tree invokes the
hotplug notifier chain.

This change is needed because of the change in the way memory is
represented under the ibm,dynamic-reconfiguration-memory node.  All lmbs
are described in the ibm,dynamic-memory property instead of having a
separate node for each lmb as in previous device tree layouts.  This
requires the update_node() routine to check for updates to the
ibm,dynamic-memory property and invoke the hotplug notifier chain.

This also updates the pseries hotplug notifier to be able to gather information
for lmbs represented under the ibm,dynamic-reconfiguration-memory node and
have the lmbs added/removed.

Signed-off-by: Nathan Fontenot <nfont@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>