qemu: Don't query unavailable-features if qom-list-get is supported

qemu: Don't query unavailable-features if qom-list-get is supported

With qom-list-get we already have the value of unavailable-features
property in the returned object (just like we have all values of all
bool properties). Let's use the value from there instead of querying for
it separately using qom-get.

After this patch only a single QMP command is used for getting all the
required info about guest CPUs created by QEMU 10.1 or newer.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>