intel_perf_counters: Add support for Sandybridge.

While the Sandybridge PRM doesn't have any documentation on the GPU's
performance counters, a lot of information can be gleaned from the older
Ironlake PRM.  Oddly, none of the information documented there actually
appears to apply to Ironlake.  However, it apparently works just great
on Sandybridge.

Since this information has all been publicly available on the internet
for around three years, we can use it.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
1 file changed