qapi: Mark deprecated QMP parts with feature 'deprecated'

Add feature 'deprecated' to the deprecated QMP commands, so their
deprecation becomes visible in output of query-qmp-schema.  Looks like
this:

    {"name": "query-cpus",
     "ret-type": "[164]",
     "meta-type": "command",
     "arg-type": "0",
---> "features": ["deprecated"]}

Management applications could conceivably use this for static
checking.

The deprecated commands are change, cpu-add, migrate-set-cache-size,
migrate_set_downtime, migrate_set_speed, query-cpus, query-events,
query-migrate-cache-size.

The deprecated command arguments are block-commit arguments @base and
@top, and block_set_io_throttle, blockdev-change-medium,
blockdev-close-tray, blockdev-open-tray, eject argument @device.

The deprecated command results are query-cpus-fast result @arch,
query-block result @dirty-bitmaps, query-named-block-nodes result
@encryption_key_missing and result @dirty-bitmaps's member @status.
Same for query-block result @inserted, which mirrors
query-named-block-nodes.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200317115459.31821-27-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>