Deprecate QMP `cpu-add`

The intended functionality of QMP `cpu-add` is replaced with
`device_add` (and `query-hotpluggable-cpus`).  So let's deprecate
`cpu-add`.

A complete example of vCPU hotplug with the recommended way (using
`device_add`) is provided as part of a seperate docs patch.

Suggested-by: Eduardo Habkost <ehabkost@redhat.com
Signed-off-by: NKashyap Chamarthy <kchamart@redhat.com>
Message-Id: <20181030123526.26415-2-kchamart@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qapi/misc.json

@@ -1109,7 +1109,7 @@
 ##
 # @cpu-add:
 #
-# Adds CPU with specified ID
+# Adds CPU with specified ID.
 #
 # @id: ID of CPU to be created, valid values [0..max_cpus)
 #
@@ -1117,6 +1117,10 @@
 #
 # Since: 1.5
 #
+# Note: This command is deprecated.  The `device_add` command should be
+#       used instead.  See the `query-hotpluggable-cpus` command for
+#       details.
+#
 # Example:
 #
 # -> { "execute": "cpu-add", "arguments": { "id": 2 } }
@@ -3219,6 +3223,8 @@
 ##
 # @query-hotpluggable-cpus:
 #
+# TODO: Better documentation; currently there is none.
+#
 # Returns: a list of HotpluggableCPU objects.
 #
 # Since: 2.7

qemu-deprecated.texi

@@ -121,6 +121,11 @@ replaced by the ``target'' output member.
 The @option{[hub_id name]} parameter tuple of the 'hostfwd_add' and
 'hostfwd_remove' HMP commands has been replaced by @option{netdev_id}.
 
+@subsection cpu-add (since 3.1)
+
+Use ``device_add'' for hotplugging vCPUs instead of ``cpu-add''.  See
+documentation of ``query-hotpluggable-cpus'' for additional details.
+
 @section System emulator devices
 
 @subsection ivshmem (since 2.6.0)