sync_qemu_models_i386: Add support for versioned CPU models

sync_qemu_models_i386: Add support for versioned CPU models

Each CPU model with -v* suffix is defined as a standalone model copying
all attributes of the previous version. CPU model versions with an alias
are handled differently. The full definition is used for the alias and
the versioned model is created as an identical copy of the alias.

To avoid breaking migration compatibility of host-model CPUs all
versioned models are marked with <decode guest='off'/> so that they are
ignored when selecting candidates for host-model. It's not ideal but not
doing so would break almost all host-model CPUs as the new versioned CPU
models have all vmx-* features included since their introduction while
existing CPU models were updated later. This meas existing models would
be accompanied with a long list of vmx-* features to properly describe a
host CPU while the newly added CPU models would have those features
enabled implicitly and their list of features would be significantly
shorter. Thus the new models would always be better candidates for
host-model than the existing models.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>