Cons:
- it was only integrated in r600g
- it doesn't work with GPUVM
- it records buffer contents at the end of IBs instead of at the beginning,
  so the replay isn't exact
- it lacks an IB parser and user-friendliness

A better solution is apitrace in combination with gallium/ddebug, which
has a complete IB parser and can pinpoint hanging CP packets.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>