powerpc/cacheinfo: Warn if cache object chain becomes unordered

This can catch cases where the device tree has gotten mishandled into
an inconsistent state at runtime, e.g. the cache nodes for both the
source and the destination are present after a migration.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190627051537.7298-5-nathanl@linux.ibm.com