CSVT: Introduce Circuit-Switch Video Telephony.

    Introduce CSVT Service which provides necessary API
    for Circuit-Switch Video Telephony.

Change-Id: I1d483212450720d64d05f4e2b02abf8da9f4b37e
(cherry picked from commit dc5000ac8e63e4009cb7a17c3d01aaa88353ed11)
(cherry picked from commit 93fcbbd2de9ff1ef4366ee25eea6c2ad3fb37d3c)
(cherry picked from commit 07b42287c38f0d280bd593288b2d152392272eef)