powerpc/pseries: reset the RCU watchdogs after a LPM

The RCU watchdog timer should be reset when restarting the CPU after a
Live Partition Mobility operation.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Combine comments into a single comment block]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221125173204.15329-1-ldufour@linux.ibm.com