Update PowerHAL documentation to clarify Session ID size restriction

    /**

     * The session's unique ID, used to identify the session for debugging and

     * for multiplexing on the per-process FMQ channel.

     *

     * Values that fit in the 32-bit int range value must be provided when using

     * the FMQ API, as the FMQ messages can only accept 32-bit Session IDs.

     */

    long id;

}