ppc/pnv: Extend chip_pir class method to TIR as well

ppc/pnv: Extend chip_pir class method to TIR as well

The chip_pir chip class method allows the platform to set the PIR
processor identification register. Extend this to a more general
ID function which also allows the TIR to be set. This is in
preparation for "big core", which is a more complicated topology
of cores and threads.

Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>