- OMXAndroid_EnableGraphicBuffers: activate GraphicBuffers.
  Next call of OMX_GetParameter(OMX_IndexParamPortDefinition) will return a
  private eColorFormat compatible with android hal_format.

- OMXAndroid_GetGraphicBufferUsage: return hw_usage that will be used to
  allocate android hw buffers.
Signed-off-by: Martin Storsjö <martin@martin.st>