ppc/pnv: Change powernv default to powernv10 POWER10 is the latest IBM Power machine. Although it is not offered in "OPAL mode" (i.e., powernv configuration), so there is a case that it should remain at powernv9, most of the development work is going into powernv10 at the moment. Reviewed-by: Cédric Le Goater <clg@kaod.org> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>