GraphicBufferSource fixes

Various fixes:
- Set the maximum number of BQ buffers we're allowed to
  acquire equal to the actual number of codec buffers.  That
  way we keep the codec as full as possible, and never try to
  acquire more than we're allowed from the BufferQueue.
- Actually use "end of stream sent" flag.
- Name the BufferQueue (for debug messages).

Bug 8359403

Change-Id: I3b8c1f679bbebf6a89e623e13ca029eda7f657ba