This flag was used to support the PHB4 LSIs on P9 DD1 and we have
stopped supporting this CPU when DD2 came out. See skiboot commit:

  https://github.com/open-power/skiboot/commit/0b0d15e3c170Signed-off-by: NCédric Le Goater <clg@kaod.org>
Reviewed-by: NGreg Kurz <groug@kaod.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201210171450.1933725-10-clg@kaod.org