Our driver implementation is known to decrease performance for some tests,
but we don't know if any apps and benchmarks (e.g. those tested by Phoronix)
are affected. This disables the feature just to be safe.

Set this to enable partial primitive binning:
    R600_DEBUG=dpbb
Set this to enable full primitive binning:
    R600_DEBUG=dpbb,dfsm

v2: add new debug options

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