Support VP8 encoder key frame interval and number of

temporal layers configuration.

- Change ACodec.cpp to populate VP8 extra parameters
structure with key frame interval, number of temporal
layers and quantization parameters.

- Change software VP8 encoder to select frame temporal
patterns and temporal layers bitrate distribution based
on the number of layers similar to patterns used in WebRTC.

- Calculate video frame duration in VP8 encoder from the
timestamps.

Bug: 11969958
Change-Id: Ia96054d886cd09d8c108dfe250fc5f4478eaa042