target-i386: Fold -cpu ?cpuid, ?model output into -cpu help, drop ?dump

target-i386: Fold -cpu ?cpuid, ?model output into -cpu help, drop ?dump

Commit c8057f95 (accidentally) disabled the ability to pass
option strings starting with '?' to the target-specific
cpu_list function, so the target-i386 specific "-cpu ?dump",
"-cpu ?cpuid" and "-cpu ?model" stopped working.

Since these options are undocumented and not used by libvirt,
simply drop them completely rather than reinstating them
with new style syntax. Instead, we fold the ?model and ?cpuid
output into the output of the plain "-cpu help" output. The
detailed output produced by ?dump is dropped.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>