qapi: Make CpuModelExpansionInfo::deprecated-props optional and generic

qapi: Make CpuModelExpansionInfo::deprecated-props optional and generic

We'd like to have some unified QAPI schema. Having a structure field
conditional to a target being built in is not very practical.

While @deprecated-props is only used by s390x target, it is generic
enough and could be used by other targets (assuming we expand
CpuModelExpansionType enum values).

Let's always include this field, regardless of the target, but make it
optional. This is not a compatibility break only because the field
remains present always on S390x.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-ID: <20250522190542.588267-9-pierrick.bouvier@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>