docs/system/cpu-hotplug: Update example's socket-id/core-id

docs/system/cpu-hotplug: Update example's socket-id/core-id

The example of how to do vCPU hotplug and hot-unlpug in the
cpu-hotplug documentation no longer works, because the way we
allocate socket-id and core-id to CPUs by default has changed at some
point.  The output also no longer matches what current QEMU produces
in some more cosmetic ways.

Update the example to match current QEMU. The differences are:
 * the second CPU is now socket-id=0 core-id=1,
   not socket-id=1 core-id=0
 * the order of fields in QMP responses is now in alphabetical order
 * the "arch" member is no longer present in the query-cpus-fast
   output (it was removed in QEMU 6.0)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Message-id: 20241010131800.3210161-1-peter.maydell@linaro.org
Message-id: 20240819144303.37852-1-peter.maydell@linaro.org