Switch to a more extensible annotation system for RPC protocols

Switch to a more extensible annotation system for RPC protocols

Currently the RPC protocol files can contain annotations after
the protocol enum eg

   REMOTE_PROC_DOMAIN_SNAPSHOT_LIST_CHILDREN_NAMES = 247, /* autogen autogen priority:high */

This is not very extensible as the number of annotations grows.
Change it to use

    /**
     * @generate: both
     * @priority: high
     */
   REMOTE_PROC_DOMAIN_SNAPSHOT_LIST_CHILDREN_NAMES = 247,

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>