[Mesa-dev] Gen6+ transform feedback fully in hardware

[Kenneth Graunke]

This series deletes all the software primitive counting used to compute
transform feedback buffer offsets, and generally cleans up all of that
code.  Now that we require hardware contexts on Gen6+, we can just
initialize the counters to 0 and let the hardware do the counting for us.

This means that we get hardware primitive restart in the majority of cases,
which should be a lot more efficient.  It also means we're prepared for
geometry shaders.