target-ppc: Make host CPU a subclass of the host's CPU model

This avoids assigning individual class fields and contributors
forgetting to add field assignments in KVM-only code.

ppc_cpu_class_find_by_pvr() requires the CPU model classes to be
registered, so defer host CPU type registration to kvm_arch_init().

Only register the host CPU type if there is a class with matching PVR.
This lets us drop error handling from instance_init.

Signed-off-by: Andreas Färber <afaerber@suse.de>
target-ppc: List alias names alongside CPU models

Revert adding a separate -cpu ? output section for aliases and list them
per CPU subclass.

Requested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Andreas Färber <afaerber@suse.de>
target-ppc: Report CPU aliases for QMP

The QMP query-cpu-definitions implementation iterated over CPU classes
only, which were getting less and less as aliases were extracted.

Keep them in QMP as valid -cpu arguments even if not guaranteed stable.

Signed-off-by: Andreas Färber <afaerber@suse.de>
target-ppc: Move CPU aliases out of translate_init.c

Move array of CPU aliases to cpu-models.c, alongside model definitions.
This requires to zero-terminate the aliases array since ARRAY_SIZE() can
no longer be used in translate_init.c then.

Suggested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Andreas Färber <afaerber@suse.de>