pseries/drmem: update LMBs after LPM

After a LPM, the device tree node ibm,dynamic-reconfiguration-memory may be
updated by the hypervisor in the case the NUMA topology of the LPAR's
memory is updated.

This is handled by the kernel, but the memory's node is not updated because
there is no way to move a memory block between nodes from the Linux kernel
point of view.

If later a memory block is added or removed, drmem_update_dt() is called
and it is overwriting the DT node ibm,dynamic-reconfiguration-memory to
match the added or removed LMB. But the LMB's associativity node has not
been updated after the DT node update and thus the node is overwritten by
the Linux's topology instead of the hypervisor one.

Introduce a hook called when the ibm,dynamic-reconfiguration-memory node is
updated to force an update of the LMB's associativity. However, ignore the
call to that hook when the update has been triggered by drmem_update_dt().
Because, in that case, the LMB tree has been used to set the DT property
and thus it doesn't need to be updated back. Since drmem_update_dt() is
called under the protection of the device_hotplug_lock and the hook is
called in the same context, use a simple boolean variable to detect that
call.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210517090606.56930-1-ldufour@linux.ibm.com