MediaCas: combine openSession methods

    virtual status_t setPrivateData(

            const CasData &privateData) = 0;

    // Open a session for descrambling a program. The session will receive the

    // ECM stream corresponding to the CA_PID for the program.

    virtual status_t openSession(

            uint16_t program_number,

            CasSessionId *sessionId) = 0;

    // Open a session for descrambling an elementary stream inside a program.

    // The session will receive the ECM stream corresponding to the CA_PID for

    // the stream.

    virtual status_t openSession(

            uint16_t program_number,

            uint16_t elementary_PID,

            CasSessionId *sessionId) = 0;

    // Open a session for descrambling a program, or one or more elementary

    // streams.

    virtual status_t openSession(CasSessionId *sessionId) = 0;

    // Close a previously opened session.

    virtual status_t closeSession(

            const CasSessionId &sessionId) = 0;

    virtual status_t closeSession(const CasSessionId &sessionId) = 0;

    // Provide the CA private data from a CA_descriptor in the program map

    // table to a CasPlugin.