target/ppc: Return default CPU for max CPU

target/ppc: Return default CPU for max CPU

All ppc CPUs represent hardware that exists in the real world, i.e.: we
do not have a "max" CPU with all possible emulated features enabled.
Return the default CPU type for the machine because that has greater
chance of being useful as the "max" CPU.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1038
Cc: Cédric Le Goater <clg@kaod.org>
Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: Greg Kurz <groug@kaod.org>
Cc: Matheus K. Ferst <matheus.ferst@eldorado.org.br>
Cc: Thomas Huth <thuth@redhat.com>
Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Víctor Colombo <victor.colombo@eldorado.org.br>
Message-Id: <20220628205513.81917-1-muriloo@linux.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>