ppc/pnv: SMT support for powernv

ppc/pnv: SMT support for powernv

Set the TIR default value with the SMT thread index, and place some
standard limits on SMT configurations. Now powernv is able to boot
skiboot and Linux with a SMT topology, including booting a KVM guest.

There are several SPRs and other features (e.g., broadcast msgsnd)
that are not implemented, but not used by OPAL or Linux and can be
added incrementally.

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Tested-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-ID: <20230705120631.27670-4-npiggin@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>