stagefright: remove OMXNodeInstance usage from GraphicBufferSource

This is a preliminary to separate GraphicBufferSource from IOMX.

- Use IOMX instead of internal OMXNodeInstance.

- Keep track of codec buffers by buffer_id, do not write to the
  OMX buffer headers directly

- Upon data space change, notify IOMX to handle it

bug: 31399200

Change-Id: I86534d7602294f70da582457b5af2eb9b6a58eda