target-i386: X86CPU model subclasses

Register separate QOM types for each x86 CPU model.

This will allow management code to more easily probe what each CPU model
provides, by simply creating objects using the appropriate class name,
without having to restart QEMU.

This also allows us to eliminate the qdev_prop_set_globals_for_type()
hack to set CPU-model-specific global properties.

Instead of creating separate class_init functions for each class, I just
used class_data to store a pointer to the X86CPUDefinition struct for
each CPU model. This should make the patch shorter and easier to review.
Later we can gradually convert each X86CPUDefinition field to lists of
per-class property defaults.

The "host" CPU model is special, as the feature flags depend on KVM
being initialized. So it has its own class_init and instance_init
function, and feature flags are set on instance_init instead of
class_init.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>