A few fixes in SW VP8 encoder:

- Increase encoder output buffer size to 1 Mb to avoid buffer
  overrun when encoding high complexity HD frames.

- Store output port format parameters.

- Use same VP8 encoder settings as in WebRTC when encoder is
  configured to run in CBR mode.

Bug: b/12924516
Bug: b/12908952
Change-Id: Ida884efd0cd1a7272998f5835abd290bfb19b2ac