qom: introduce object_class_get_list_sorted

Unify half a dozen copies of very similar code (the only difference being
whether comparisons were case-sensitive) and use it also in Tricore,
which did not do any sorting of CPU model names.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>